Developments in Libya and the death of Muammar Gaddafi have spurred on Yemen's protest movement [EPA]

Yemeni troops loyal to President Ali Abdullah Saleh have opened fire on thousands of protesters calling for his
removal, killing six and wounding dozens more, sources say.

The demonstration was taking place since the early morning hours in the capital, Sanaa, on Tuesday, with protesters marching through the streets surrounding Change Square, the epicentre of the nationwide movement calling for Saleh's resignation.

The protesters were marching towards Sanaa's Al-Qaa district, an area controlled by pro-Saleh troops, when they were fired upon with live ammunition, witnesses told the AFP news agency.

Three of the dead reportedly reached a field hospital run by the revolutionary doctors, while three other bodies were taken to the state-run Al Jumhuri hospital in the capital, sources told Al Jazeera.

"The people want to prosecute the butcher," the Associated Press news agency quoted the protesters as chanting. They were demanding a trial for Saleh.

Some also held up posters saying that after the death of Libya's Muammar Gaddafi, it was time for Saleh to "listen to your people".

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Amid the shooting, the marchers were forced to retreat from the surrounding streets towards Change Square, AP said.

Saleh's forces in Sanaa have exchanged gunfire with troops from renegade army units lead by Major-General Ali Mohsen al-Ahmar, who defected to the opposition early on in the uprising and whose forces now escort and protect the protesters.

Mohammed al-Qubati, who runs a field hospital at the protesters' camp site, said at least 40 people were wounded by Saleh's forces during Tuesday's shooting.

He said dozens also suffered breathing difficulties because of tear gas fired by the troops and several passed out.

Violence in Sanaa has escalated in the wake of a non-binding UN Security Council resolution urging Saleh to sign a Gulf states-brokered deal that paves the way for his resignation.

Saleh welcomed the resolution on Monday, but has so far refused to sign the agreement, despite increased regional and international pressure to do so.

Meanwhile, in Yemen's second largest city Taiz, seven civilians died and at least 30 others were wounded in shelling and in clashes between armed tribesmen who back the anti-government protesters and pro-Saleh troops, medics and sources told Al Jazeera.

Witnesses there described scenes of fear and chaos as mortar shells fell randomly on city neighbourhoods overnight and early on Tuesday, damaging dozens of houses and forcing schools to shut down.