Yemeni security forces have opened fire on anti-government demonstrators in the capital Sanaa, killing at least 16 people and wounding dozens more, medics said.
Security forces used live rounds as well as tear gas and water cannon to disperse thousands of people attempting to march on the city centre from their stronghold in Change Square, witnesses said on Saturday.
Protesters have been gathering in Sanaa for months to demand the resignation of Ali Abdullah Saleh, the embattled Yemeni president who continues to defy domestic and international pressure to quit.
Our special correspondent in Yemen said a huge rally was marching along a road in the north of the city towards the centre when they were attacked by government supporters.
"It started off with a few sporadic shots with Kalashnikov [rifles], then the sound of heavy machine guns and heavy mortars," our correspondent said.
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"I have seen people rushed into the back of cars with blood pouring from their chests.
The protesters marched on, despite the shooting, reaching the Zubeiri (also known as Kentucky) roundabout, where clashes have repeatedly taken place over the last several weeks.
Our correspondent said that the protesters were carrying olive leaves and none of them had appeared to be armed.
'Batons and rocks'
He said that he had seen "plain clothes pro-government loyalists being armed with batons and rocks" before the attack on the rally took place.
At a hospital where the injured were being treated, medical authorities had run out of beds and were appealing for more supplies, particularly bandages and IV drips.
Tariq Noman, the chief surgeon at a field hospital in Sanaa, confirmed that they have received the bodies of protesters who were shot by security forces, as well as treated more than 100 injured people.
Noman told Al Jazeera that most of the dead were shot by snipers in the head, the chest and neck. Severla other hospitals and medicl facilities said they had received bodies and were treating the wounded.
"What [the medical staff have] started doing is trying to shift some of the people who have been injured to other hospitals around the capital so that they can get proper treatment," our special correspondent said.
"But it's difficult, there are lots of soldiers on the streets of Sanaa today. There are checkpoints at nearly every major intersection, so even ambulances have been having difficulty getting the injured treated and getting them to hospitals quickly.
"Sanaa is a very tense place to be at the moment. This was a huge protest that took place today, and I think it just completely overwhelmed the security forces."
State television reported that protesters had opened fire on civilians after taking out an "unauthorised" protest from Sitin Street to the Aser area.
The Saba news agency, citing an interior ministry official, reported that two members of the government's security forces had been killed and 16 more wounded in clashes accompanying Saturday's protest.
In separate violence, forces loyal to Saleh's elite Republican Guard unit clashed with soldiers who had sided with protesters, our correspondent said.
At least four people were killed in those clashes, with a further 13, including at least six civilians, wounded.
Doctors told Al Jazeera that they were in need of international help, our correspondent reported.
"A lot of Yemenis feel that the international community has been applying double standards: paying a lot of attention to Libya and Syria, but not really issuing really strong condemnations [on Yemen]."
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 began earlier in the year.
The government has urged the UN Security Council to avoid a resolution targeting Saleh, which protesters have asked for.
Saleh has promised several times to abide by a Gulf Co-operation Council-backed plan to hand over power to his deputy, but has so far failed to do so.
In separate developments on Saturday, the Yemeni Defence Ministry said that al-Qaeda's media chief was killed in an airstrike, and a key gas pipeline was blown up.