|Anti-government protesters were hit by sniper fire and shrapnel during Sunday's demonstrations in Sanaa [Reuters]
Troops loyal to Yemeni President Ali Abdullah Saleh and forces opposed to his rule have been engaged in heavy fighting across much of the capital, Sanaa, with rockets, mortars and heavy machine guns.
The fighting began shortly after midnight on Monday and intensified into the early hours of the morning, with the sound of explosions rocking many parts of the city.
There were no overall casualty figures immediately available, but at least eight people were killed in a central encampment housing tens of thousands of protesters.
A journalist who is based in Sanaa told Al Jazeera the situation "is a very volatile situation, many of the streets of Sanaa are empty this morning".
According to medical officials, six people were also wounded when a shell hit their house in an area in the northern part of the capital.
Fighting died down when the call for the Muslim dawn prayer rang out from the city's mosques, but resumed a short time afterward.
Pro-Saleh forces have frequently fought with rival tribesmen and renegade troops of the 1st Armoured Division in Sanaa, but Monday's fighting was the most intense in weeks, with the pro-regime forces shelling their rivals' positions from the hills outside the city.
On Sunday at least 13 protesters and pro-revolution forces were killed during a demonstration in the Yemeni capital by troops loyal to Saleh.
The protesters were hit by sniper fire and shrapnel from rocket-propelled grenades, a Yemen based journalist reported from Sanaa.
"A lot of the victims were either shot in the head of the chest, typical for wounds inflicted by snipers," the
On Saturday, 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.
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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 the 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.
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.