Medics report at least 13 deaths as pro-government forces fire on protesters in the capital, Sanaa.
At least five protesters and seven pro-revolution soldiers have been killed during a demonstration in the Yemeni capital by troops loyal to President Ali Abdullah Saleh.
The protesters were hit by sniper fire and shrapnel from rocket-propelled grenades, Al Jazeera's special correspondent reported from Sanaa on Sunday.
"A lot of the victims were either shot in the head of the chest, typical for wounds inflicted by snipers," our correspondent said.
The violence came as Yemeni pro-democracy activists called for a new mass demonstration aimed at bringing 10 months of protests to a head.
The previous day, troops fatally shot at least 17 people marching in Sanaa.
"We will continue with our protests ... even if thousands of our youth are killed. This is the only way to ensure the fall of the regime," Walid al-Ammari, a spokesman for the protesters, told the AFP news agency.
Ammari said activists were planning a fresh march on areas of Sanaa controlled by troops loyal to Saleh from their base in Change Square.
They hope to reach within a kilometre of the presidential palace, a move that could provoke another deadly response from the security forces.
Our special correspondent in Yemen reported that the field hospital was completely full with latest casualties, saying that "this is another day of bloodshed in Yemen where unarmed protesters are caught in the middle of Pro-Saleh forces and defected soldiers".
They hope to reach within a kilometre of the presidential palace, a move that could provoke another deadly response from the security forces.
Our special correspondent in Yemen reported that the field hospital was completely full with latest casualties, saying that "this is another day of bloodshed in Yemen where unarmed protesters are caught in the middle of Pro-Saleh forces and defected soldiers".
Sunday's violence erupted when hundreds of thousands of protesters marched on Al-Zubeiri Street which marks the dividing line between parts of Sanaa held by troops loyal to Saleh and those held by dissident units under the command of General Ali Mohsen al-Ahmar, who rallied to the opposition in March.
According to a letter from Yemen's youth movement to the United Nations, sent earlier this month, at least 861 people have been killed and more than 25,000 wounded since mass protests against Saleh's rule began earlier in the year.
According to a letter from Yemen's youth movement to the United Nations, sent earlier this month, at least 861 people have been killed and more than 25,000 wounded since mass protests against Saleh's rule began earlier in the year.
The ongoing clashes have stalled a Gulf Co-operation Council (GCC) initiative that would lead to Saleh stepping down and handing over all constitutional authorities to his deputy.
Under the plan, Saleh and his family were to be granted immunity from prosecution.
Saleh has promised several times in the past to abide by the initiative, but has so far failed to do so.
He called for a truce and new negotiations on his return to Sanaa after three months in Saudi Arabia where he recovered from a June 3 attack on his presidential compound.
The president has faced protests since January over nepotism and corruption from reform activists inspired by the Arab Spring.
Saleh has promised several times in the past to abide by the initiative, but has so far failed to do so.
He called for a truce and new negotiations on his return to Sanaa after three months in Saudi Arabia where he recovered from a June 3 attack on his presidential compound.
The president has faced protests since January over nepotism and corruption from reform activists inspired by the Arab Spring.
