Yemen unrest: Death toll from Sanaa clashes tops 50
Security forces in Yemen have killed more than 50 people in two days of violence against anti-government protesters, activists say, in the country's bloodiest clashes for months.
Snipers in Sanaa fired from rooftops at a protester camp, killing bystanders including a child, witnesses said.
Government forces also shelled areas held by troops loyal to the protesters.
The opposition has promised to carry on its campaign to oust President Ali Abdullah Saleh.
For months, thousands of people have been waging a campaign to depose Mr Saleh, who has ruled the country since 1978 and is currently in Saudi Arabia recovering from a bomb attack in June.
The opposition believes the government is deliberately orchestrating the violence to derail any chance of agreement.
But a Yemeni minister strongly denied reports that the authorities had fired on peaceful demonstrators, telling the BBC government forces were being attacked by militants sympathetic to al-Qaeda.
The US and EU nations were among members of the UN Human Rights Council who used a meeting in Geneva on Monday to urge Yemen's government to stop using force against protesters.
Meanwhile, as the violence intensified, envoys from the UN and the Gulf Co-operation Council arrived in Yemen, in a new attempt to negotiate a handover of power from Mr Saleh.
The last two days have seen the worst violence in the country for several months: on Sunday, 26 people were killed and many more injured as they marched towards the presidential palace in Sanaa, the capital.
But protest leaders issued a rallying cry urging more demonstrations on Monday, in which at least 27 people died as security forces once again opened fire on civilians.
Reports say snipers began firing at a protest camp shortly after leaders of the demonstrations had begun to use loud-hailers to urge more action.
The snipers killed several people - among them a child who was unconnected with the protests - activists said.
The boy's father told the Reuters news agency: "I stepped out to get some food and left my two boys in the car and I heard the older one scream. The little one was shot straight through the head."
In another part of the city, a firefight broke out between government troops and soldiers loyal to the protesters.
Hakim al-Masmari, editor of the Yemen Post in Sanaa, told the BBC that military planes were regularly flying over the city, attacking positions held by defected troops. Witnesses reported an air raid on a military base containing soldiers who had switched allegiance.
Tom Finn, a freelance reporter in Sanaa, said on Twitter that injured people were arriving at a makeshift hospital "by the dozen", most of them with gunshot wounds to the legs.
And witnesses reported that government troops were shelling areas of the city guarded by troops loyal to the protesters.
More deaths were also reported in the city of Taiz, south of the capital.
Yemen's Minister of Trade and Industry, Hisham Sharaf, told the BBC the clashes were initiated by al-Qaeda-linked forces within the opposition who do not want a political solution to be reached.
"The government of Yemen and Vice President Abdul Abedrabbo Mansour gave orders to not shoot at any civilian person having a demonstration," he told the BBC's Newshour programme.
"But anyone who has a gun or a bazooka or is shooting from a vehicle, with live ammunition. What do you expect the police to do? Just to look at them?"
The UK has condemned the deadly response to Sunday's protests, calling on all sides to "disengage forces immediately and avoid escalation".
Conceding that the UK's ability to increase pressure for political reform in Yemen were "relatively limited", Foreign Secretary William Hague told Sky News: "We will be intensifying all those efforts over the coming days."
Meanwhile, the UK-based charity Oxfam is warning that Yemen is at breaking point and faces a food crisis.
"A protracted political stalemate over much of the past six months has left the government in paralysis, prompting a fuel crisis that has brought the economy to the verge of collapse," says the charity in a new report.
Oxfam warned that 7.5 million Yemenis - one third of the population - are going hungry and said the international community needed to step up its aid response.