The line dividing Christians from Muslims that runs along a rocky valley in the central Nigerian town of Jos may not be visible to the eye, but it burns in the minds of local people.
The mosque lies barely 200 metres (yards) from the main church in the Congo-Russia neighbourhood, a huddle of tin-roofed homes winding up a hill, and on its sandy pavements women in Muslim headscarves politely greet men wearing shiny crucifixes.
Jos, in Nigeria's volatile Middle Belt, is historically a religious and ethnic tinderbox in the country's sensitive North-South divide between Muslims and Christians.
Deadly Christmas Day bomb attacks by shadowy Islamist sect Boko Haram - suspected of links to al Qaeda and with ambitions to impose Islamic sharia law in Nigeria - have stoked fears again of sectarian conflict in Africa's top oil producer and most populous state.
Over there's the dividing line, said trader Anthony Baya, 30, nodding at some houses cloaked in a haze of windborne dust.
You can't just go over to that place as a Christian. The Muslims can kill you, he said, describing how six youths were hacked to death with machetes and dumped down a well during Jos's last bout of inter-communal violence in November.
Nigeria's 160 million people are roughly divided between Muslims and Christians, who mostly live side by side in peace.
But towns like Jos, where ruined buildings with charred walls sprouting weeds testify to past violence, and other flashpoints bear the material and mental scars of bouts of sectarian strife that have periodically bloodied Nigeria since its independence from Britain in 1960.
The Congo-Russia neighbourhood itself is named after the Congolese and Russian U.N. peacekeepers who kept the two communities from each other's throats during Nigeria's civil war in the 1960s.
Boko Haram claimed three bomb attacks on churches on Christmas Sunday, including one that killed 27 worshippers in a Catholic church just outside the capital Abuja, and one in Jos without fatal victims.
The coordinated strikes by the northern-based Islamist group, whose name translates as Western education is sinful in the Hausa language of the region, appeared aimed at prising open Nigeria's religious faultline in a direct challenge to the government of President Goodluck Jonathan, a Christian southerner.
Boko Haram is seeking to provoke retaliatory attacks on Muslims in predominantly Christian parts of the country, said former U.S. ambassador to Nigeria John Campbell, who is the Ralph Bunche senior fellow for Africa policy studies at the Council on Foreign Relations (CFR) in New York.
FEARS OF BACKLASH
In Jos, local Muslims were wary of a possible Christian backlash.
We are just beginning to live in peace, so we hope our Christian brothers can help us keep that peace, said Mohammed Kabir, who like many Nigerian Muslims resents being associated with violent extremism. Boko Haram is not all Islam.
Stirring such fears, unknown attackers late on Tuesday lobbed a crude homemade bomb into a madrassa, or Islamic school, in Nigeria's southeastern Delta state, wounding seven people including six young children.
For some, such as Papa Jimba, 46, leader of the Christian community in Jos's Congo-Russia neighbourhood, the Boko Haram bombings have rekindled the idea of partitioning the country along religious lines.
Let us divide Nigeria, said Jimba, using his hand to trace a line between two halves of his wooden bench by the roadside.
The Muslims go to their side and the Christians stay on our side. Then peace can come back. I'm even praying for that.
The latest attacks in what seems to be an escalating campaign of anti-Christian and anti-establishment violence by Boko Haram are also being linked to a long-running political power struggle in Nigeria between north and south.
There is a clear political dimension ... there are political forces at play here that are using the religious dimension as a mobilizing and amplifying force, Jennifer Giroux, Senior Researcher at the Center for Security Studies at the university of ETH Zurich, told Reuters.
Nigeria's internal politics have soured again since Jonathan assumed the presidency earlier this year after his election victory, which in the eyes of many northerners broke a tacit deal to rotate the Nigerian leadership between north and south every two terms.
More than 500 people were killed in post-election violence in the north after Jonathan's victory, reflecting long-standing northern grievances about perceived alienation and exclusion by the central government from the fruits of national oil riches, concentrated in the south.
In Jos, the bombings also have the potential to inflame local rivalries that are really about land, ethnicity and power, but which have taken on a religious dimension that local politicians have a habit of using to settle scores.
DECLARATION OF WAR ON CHRISTIANS
The late deposed Libyan strongman Muammar Gaddafi, who had long coveted ambitions of leading Africa, suggested in March 2010 that Nigeria split into ethnic regions. The idea sparked outrage at the time, but has gained currency in some circles.
People thought Gaddafi was mad, but I've started to see the sense in what he said. If we can't exist together with our Muslim brothers, then they can build their houses over there, and we build ours here, said Reverend Philip Mwelbish, head of the Christian Association of Nigeria (CAN) for Plateau State, where Jos is located.
We have a proverb in Nigeria: if you push a goat to the wall, he will bite you. They've pushed us to the wall, Mwelbish said, before taking a Reuters team out into his farmyard flanked by Jos's jagged cliffs and volcanic boulders.
Grazing there were three cows he said he had received from Muslim leaders as Christmas presents.
Ayo Oritsejafor, CAN's national head, told President Jonathan on Wednesday that the bombs were a declaration of war on Christians, and accused Muslim clerics of failing to take responsibility for their followers.
Muslim leaders retort that they are not to blame for the actions of a few extremists in the name of Islam.
At the green, yellow and white painted Central Mosque on Jos's busiest street, Christian and Muslim leaders met on Tuesday in an effort to calm tensions.
They should understand that we don't consider the authors of these attacks to be Muslims, the mosque's spokesman Sani Mudi told Reuters after the meeting. What are their teachings? Don't forget Islamic scholars have been killed by them too.
Concentrated mainly in the northern Nigerian states of Yobe, Kano, Bauchi, Borno and Kaduna, Boko Haram became active in about 2003 and is loosely modelled on the Taliban movement in Afghanistan. It considers all who do not follow its strict ideology as infidels, whether they are Christian or Muslim, and its followers wear long beards and red or black headscarves.
The group made international headlines in July 2009 when its attacks led to clashes with Nigerian police and army in northeast cities, including its stronghold of Maiduguri. Some 800 people were killed in five days of fighting.
That same month, sect leader Mohammed Yusuf was captured by Nigerian security forces and shot dead in police detention some hours later, triggering vows of revenge by surviving adherents.
From early drive-by shootings against police officers in the remote northeast, the group has moved to more ambitious high-profile attacks, like the August 26 bombing of the U.N. headquarters in Abuja that killed at least 24 people.
AIM TO MAKE COUNTRY UNGOVERNABLE?
But while angry Christians may talk of dividing off the oil-rich south from the north, the prospect of an all-out civil war splitting Nigeria into two countries is considered unlikely.
Many acknowledge it would be virtually impossible to separate peoples already so woven together.
All northern states have substantial Christian minorities and up to half of Nigeria's more than 30-million strong southwestern Yoruba ethnic group are thought to be Muslim, although nobody knows the real figure.
Many families in the Middle Belt are mixed Muslim and Christian. Jos resident John Amasa, 21 - his Muslim name is Jamilu Amasa - has a Muslim father and a Christian mother.
Though he chose to be Christian, he feels strong ties to Islamic culture too.
If this country splits, where do my parents go? Where do I go? he said. We'd rather die than be separated.
That any such attempted split would be catastrophic is one thing most Nigerians agree on, regardless of religion. The country has already experienced a civil war, the bloody conflict over the secession of Biafra in the 1960s that killed at least a million people and caused mass starvation.
We have fought a civil war and everybody saw how damaging that was. We are still recovering from it, said Plateau state publicity secretary for the opposition Labour Party, Sylvanus Namang. Nobody in this country wants to see that again.
What Boko Haram themselves really want out of this Pandora's Box of potential consequences is subject to speculation, and it is not at all clear that they really want to split the country, rather than just threaten and embarrass the central government.
Former U.S. ambassador to Nigeria Campbell believes the group is seeking to demonstrate that the country is increasingly ungovernable by the secular government in Abuja led by a Christian (Jonathan).
The attacks are indeed a form of politics. They do ram home the point that the government cannot guarantee the security of its citizens in all parts of the country, he told Reuters.
DEBATE OVER WIDER THREAT
Boko Haram spokesman Abu Qaqa was quoted in the local press on Wednesday as saying the bombs were revenge for attacks in Jos by Christian youths on Muslims during an Islamic holiday at the end of August.
The increasing apparent coordination and sophistication of the group's latest attacks have led Nigerian authorities and some western security experts to suspect growing links to wider Islamic Jihadist movements, such as al Qaeda's North African wing, AQIM.
AQIM looks to the trends in northern Nigeria as an exploitable opportunity that, with their involvement and investment, will in turn deepen the complexity of the problem and make it increasingly harder to untangle, said Giroux.
But there is some scepticism about the extent of Boko Haram's links to AQIM. Campbell for example sees enough domestic factors and grievances inside Nigeria alone to explain and sustain the insurgency.
Giroux expected there would continue to be flashpoints in Boko Haram's campaign but not something that results in full out civil war.
If anything I think Nigerians have shown tremendous resilience in the face of a movement that seeks to breed division, she said. But Giroux expected Western governments to step up counter-terrorism support for Nigeria's government.
The failure of Nigeria's police and military to end the insurgency despite many crackdowns has led many to conclude that dialogue might be the only option left -- assuming Boko Haram is not already too radicalised to be brought to the table.
The government response up to this point has been essentially a security response as opposed to a political one ... you can't stop it by treating it solely as a security matter, said Campbell.
He and others believed that Jonathan and his government should work on political initiatives reaching out to the restive north to address its religious and political grievances.
And lurking in the minds of Nigerian and foreign security experts is a growing fear: that Boko Haram will seek to carry its violent campaign into Nigeria's oil-rich south.
(Additional reporting by Pascal Fletcher in Johannesburg and Buhari Bello in Jos; Editing by Pascal Fletcher and Giles Elgood)