A suicide bomber killed about 25 people and wounded 46 in Damascus on Friday, Syria's state news agency SANA said, bringing bloodshed to the heart of the Syrian capital for the second time in two weeks.
The blast occurred two days before an Arab League committee was due to discuss an initial report of Arab observers who are checking Syria's compliance with an Arab plan to halt President Bashar al-Assad's crackdown on nearly 10 months of unrest.
The meeting may decide whether to continue the mission or to refer Syria to the United Nations Security Council, perhaps paving the way for some form of international action, a scenario that many Arab countries are keen to avoid.
Arab League chief Nabil Elaraby said he was sending a message with Damascus-based Hamas leader Khaled Meshaal asking the Syrian government to work to halt the violence.
Syrian state television showed body parts, bloodstains and broken glass from the blast in the central Maidan district. Several riot police shields could be seen in a wrecked bus, which was among several damaged vehicles.
SANA said 10 people had been killed and body parts of about 15 more had been found.
On December 23 at least 44 people were killed by what Syrian authorities said were two suicide bombings that targeted security buildings in the Syrian capital.
Those attacks occurred the day before the arrival in Damascus of the head of the Arab League observer mission.
Footage of Friday's blast on Syria's semi-official Addounia TV showed yellow tape stretched around the wrecked bus and cars with smashed windows in a street. People collected body parts on blue plastic sheets amid pools of blood and scattered shoes.
Arab monitors in white baseball caps and orange vests inspected the area, taking notes and filming. The local police station was visible, apparently untouched by the explosion.
The TV showed crowds of angry locals gathered at the scene, chanting God, Syria and Bashar only and God protect the army and With blood and soul we sacrifice for you Bashar.
A woman named Umm Mohammed said those behind the blast were attacking the security forces who protect Syrians. They (protesters) say they want freedom, this here is freedom, not those children of saboteurs, God curse them, she said.
The monitors confirmed they had visited the scene. We are only here to observe and document, one of them said.
Syria bars most independent journalists from the country, making first-hand reporting impossible.
However, a BBC Arabic service reporter was able to accompany three Arab monitors on a five-hour visit to the town of Irbine, on the outskirts of Damascus, the BBC reported.
It was the first time foreign media were known to have been able to cover the activities of the monitors directly, although media access was a condition stipulated by the Arab League.
The BBC said it had been able to film an anti-Assad protest in Irbine unhindered by the security forces.
Protesters and residents told the observers, all Algerian diplomats, of harsh treatment at the hands of the security forces. The observers then witnessed a demonstration in which the crowd demanded Assad's execution, the BBC said.
The League's special committee on Syria is due to meet in Cairo on Sunday to debate the initial findings of the observer mission, which has been criticised by Syrian activists who question its ability to assess the violence on the ground.
Elaraby, the League's secretary-general, said after meeting Meshaal in Cairo that he had given the leader of the militant Palestinian Islamist group a message for the Syrian authorities that it is necessary to work with integrity, transparency and credibility to halt the violence that is happening in Syria.
Syria has been racked by a popular uprising against Assad in which the United Nations says more than 5,000 people have been killed. The government says armed terrorists have killed 2,000 members of the security forces during the revolt.
FATE OF ARAB MISSION
The monitors began work on the streets on December 26 to try to verify whether the government was keeping its promise to pull troops and tanks out of cities and free thousands of detainees.
The Free Syrian Army (FSA), an armed opposition force composed mainly of army deserters, condemned the Maidan attack and blamed the Syrian authorities. This is planned and systematic state terrorism by the security forces of President Bashar al-Assad, FSA spokesman Major Maher al-Naimi said.
An opposition activist, who asked not to be named, said Islamist militants might have been behind the blast. I think there are hundreds of these extremists willing to fight the regime and blow themselves up in the name of jihad, he added.
One Damascus resident, who gave her name only as Dima, said the city had been tense even before the blast. Some friends who work in the security forces were warning my family since yesterday to stay at home, she said. The streets were empty.
The violence in Syria has raged unabated since the Arab monitors arrived, with scores of people reported killed.
Security forces killed four protesters in Hama on Friday when they shot at people shouting anti-Assad slogans after weekly prayers, activists said.
Pro-Assad forces also wounded at least three protesters when they fired at a crowd at a Damascus mosque in a district where a security headquarters is located, a witness said.
The witness said pro-Assad militiamen and secret police agents fired water cannon and then assault rifles after the protesters in the Kfar Souseh district refused to disperse.
I saw three people on the ground and I do not know if they are dead or alive, said the witness, who lives nearby.
Arab government sources said on Thursday the League monitors would pursue their mission in Syria, despite criticism from Qatar's prime minister that they had made mistakes.
Syrian activists say the Arab monitors have had inadequate access to trouble spots, a charge denied by Damascus.
A Hama unit of the Free Syrian Army complained that it had tried without success to meet the monitors.
We want to prove to the world that the Assad regime is lying when it says there are armed gangs here, said an FSA officer in a video posted online.
There are no armed gangs, but soldiers who have defected after we saw that the army and security forces were killing civilians and shelling people's homes with heavy artillery.
Qatar's Prime Minister Sheikh Hamad bin Jassim al-Thani, who chairs the Arab League committee on Syria, said after meeting U.N. Secretary-General Ban Ki-moon in New York on Thursday that it was the League's first monitoring mission.
I said we must evaluate the types of mistakes it made and without a shadow of a doubt I see mistakes, even though we went in to observe, not to stop the violence, he said.
(Additional reporting by Khaled Yacoub Oweis in Amman; Writing by Alistair Lyon, editing by Diana Abdallah)