Forces loyal to Yemeni President Ali Abdullah Saleh opened fire to stop tens of thousands of protesters approaching his compound in the capital Sanaa on Saturday, injuring at least 10 people, witnesses said.
In a separate incident in the south, gunmen shot dead a Briton of Yemeni origin in an attack on a vehicle belonging to an oil company, officials said, blaming highway robbers.
In Sanaa, shots rang out as the activists entered the city chanting No to immunity, at the climax of a mass march that started days earlier in the city of Taiz 200 km (125 mile) to the south, said residents.
The protesters were referring to a deal granting Saleh immunity from prosecution for his part in a violent crackdown on months of demonstrations against his 33-year rule.
Ten people were injured, some with gunshot wounds, medical workers said.
The immunity agreement, crafted by Yemen's wealthier neighbours in the Gulf Cooperation Council (GCC), was designed to ease Saleh out of power and avert civil war in a country that has seen a growing infiltration from al Qaeda and sits next to key oil shipping lanes.
Under the deal, Saleh agreed to transfer his powers to his deputy. An interim government will prepare the country for an election to replace him in February, and has promised to separate pro-Saleh troops from militiamen loyal to tribal leaders and rebel army units in Sanaa and elsewhere.
If he goes, Saleh would be the fourth leader to surrender power after mass protests that have redrawn the political map in North African and the Middle East.
Protesters, many of them young, chanted For shame, the blood of the martyrs has been sold for dollars, referring to the immunity deal, which was endorsed by a coalition of opposition parties that are part of the interim government.
Witnesses said troops loyal to Saleh spread out across the entrances of streets leading to his compound to block any attempt by protesters to approach it.
Pro-Saleh troops also used tear gas to try to turn back protesters in the Sabaeen district of the capital, the witnesses said.
Later in the day, marchers retreated and headed towards Change Square, a rallying point for the protests which began in January, they added.
Tanks, troops and armoured vehicles were deployed around the presidential compound.
Protesters want to purge the government of members of Saleh's family, who still hold key posts in the military and security forces.
BRITON KILLED BY ROBBERS, BLAST IN ADEN
The new government faces multiple challenges including lawlessness in the south, where Islamists have seized chunks of Abyan province.
Unidentified gunmen believed to be highway robbers attacked a vehicle belonging to an oil company in the southeastern Hadramout province on Saturday, killing a Briton of Yemeni origin and wounding a soldier accompanying him, a local official said.
In the southern port city of Aden, a grenade explosion killed one person and wounded five people at a market late on Friday, a local official said. Authorities believe feuding gangs were responsible, the official added.
Authorities are facing resurgent separatist sentiment in the south, formerly a socialist republic that fought a civil war with Saleh's north in 1994 after four turbulent years of formal union.
Top oil exporter Saudi Arabia shares U.S. fears that more instability could embolden al Qaeda's branch in Yemen.
(Reporting by Mohammed Ghobari; Additional reporting by Mohammed Mukhashaf in Aden; Writing by Joseph Logan and Firouz Sedarat; Editing by Andrew Heavens)