Forces loyal to outgoing Yemeni President Ali Abdullah Saleh shot dead a woman in a protest march in Taiz on Monday, witnesses and activists said, despite tanks withdrawing under a ceasefire pact.
Anti-Saleh tribesmen brandishing Kalashnikov rifles and members of the Republican Guard, led by Saleh's son Ahmed, were still on many of Taiz's streets, witnesses said.
Tanks, armoured vehicles and opposition fighters left some areas of Taiz, a hub of 10 months of unrest against Saleh's 33-year rule, but gunmen and snipers remained and had fired on demonstrators, witnesses said.
Both sides violated the ceasefire agreement. We were marching peacefully and they (Saleh's forces) shot at us yet again, medical student Hamoud al-Aklamy told Reuters.
Both sides had pulled out of parts of the city on the orders of a committee of lawmakers, set up by acting head of state Vice President Abd-Rabbu Mansour Hadi this weekend, to try to end fighting that has killed at least 20 since Thursday.
Thousands of demonstrators gathered in the centre of Taiz, some 200 km (120 miles) south of the capital Sanaa, to protest against attacks on peaceful protesters.
At least eight people in the anti-Saleh march were injured by gunmen seen shooting from rooftops, including a 20-year-old woman who died at a hospital after she was shot in the chest, doctors said.
Elsewhere in the country's south, government forces on Monday shelled sites held by Islamist militants near Zinjibar, killing four of them, a local official said.
The official said the shelling came after the militants ambushed pro-government tribal fighters and wounded two of them. Islamist militants have seized three cities in Yemen's south since March, including Zinjibar, the capital of Abyan province.
The attempts to end clashes in Taiz came less than two weeks after Saleh signed a deal to hand over power to his deputy as part of a Gulf initiative by Yemen's wealthy Arab neighbours to end protests there.
The United States has been worried that the protests, which have weakened central government control in Yemen, could allow al Qaeda to take advantage of the security vacuum and threaten the world's number one oil exporter, Saudi Arabia, next door.
Activists blamed Monday's attacks on Saleh, who they say was determined to assert his control over the army despite the accord that made him a ceremonial president with no real powers.
Saleh said he transferred his authority to the vice president, but this is a game. We won't have a new government until half of Taiz is dead, said Aklamy.
Prime Minister-designate Mohammed Basindwa, an opposition leader who is to form a unity government with Saleh's General People's Congress party, has said he would rethink his commitments under the deal if fighting in Taiz did not stop.
Although the violence had eased since Sunday, witnesses heard at least six explosions in the city on Monday.
Political crisis has frequently halted the modest oil exports Yemen uses to finance imports of basic foodstuffs, and ushered in what aid agencies deem a humanitarian crisis.
More than 100,000 people have been displaced by military conflicts in both the north and south.
(Writing by Nour Merza; Editing by Louise Ireland and Sami Aboudi)