Fresh gunfire was reported in the Syrian city of Deraa, which has been at the centre of three weeks of unrest, as the government pushed on with a crackdown against pro-democracy protesters, despite growing international condemnation.
Bodies were left lying on the streets of Deraa on Tuesday as residents sought shelter from artillery and sniper fire, witnesses said, a day after tanks rolled into the city, marking a dramatic escalation in efforts to crush the uprising.
A resident told the Associated Press that families had been unable to recover the bodies of protesters killed by gunmen loyal to President Bashar al-Assad.
"We are being subjected to a massacre," the man screamed over the telephone as cracks of gunfire reverberated in the background. "Children are being killed. We have been without electricity for three days, we have no water."
Another resident told Reuters that there had been intermittent gunfire throughout the night followed by artillery rounds and intense machine-gun fire at around 7.30 on Tuesday morning. "Sometimes you suddenly hear a burst of heavy machine-gun fire coming in all directions as though to just scare people and terrify them," he said.
He said citizens were cut off not just from the outside world but from other parts of Deraa. "A brother doesn't know what's happening to his brother and we are still besieged," he said. "They have cut off the city's inner neighbourhoods from each other and army and snipers are still encircling almost every quarter."
The foreign secretary, William Hague, issued a strongly worded attack on the violence, amid reports that deadly attacks and arrests targeting protesters were continuing. The foreign secretary urged Assad to heed calls for reform and end a brutal campaign of repression that has reportedly seen troops open fire on crowds and tanks rolling into towns and cities. His comments came as human rights groups said dozens of people were being rounded up by security forces. More than 350 people have been killed since unrest began in Syria five weeks ago.
Hague said: "I condemn utterly any violence and killings perpetrated by the Syrian security forces against civilians who are expressing their views in peaceful protests. This violent repression must stop." He accused Assad of making empty promises to ease draconian restrictions on dissenters, saying his lifting last week of a 48-year-old emergency law had failed to fulfil pledges of reform.
He said Britain was in talks with EU and UN security council partners over ways to "send a strong signal" to the Syrian government. He made no mention of sanctions but said further measures were on the table. "Words are not enough: the emergency law needs to be lifted in practice and the legitimate aspirations of the people met," he said.
The White House expressed alarm at the violence and warned it was considering sanctions. The Obama administration condemned "the brutal violence used by the government of Syria", describing it as deplorable, and adding: "The United States is pursuing a range of possible policy options, including targeted sanctions, to respond to the crackdown and make clear that this behaviour is unacceptable."
The US state department has told American citizens to leave Syria as soon as they can, and has ordered non-essential embassy staff, and all diplomatic families to leave the country.
Thousands of government troops raided thousands of homes in the Damascus suburb of Douma on Tuesday to round up suspected protesters, eyewitnesses told Nadim Houry, a Human Rights Watch Syria researcher. He said the crackdown was believed to be worse in Deraa, at the centre of the rebellion, where tanks were deployed on Monday.
He said: "An estimated 5,000 members of the security forces circled the town and went in knocking door-to-door arresting people. According to one family three members of their family were detained. They [the security forces] had a list of names that they were looking for.
"The situation in Deraa is even more worrying but unfortunately the city remains completely cut off. We know that the Syrian army with tanks and the like entered the city on Monday morning. There are no available details at this stage of exactly what's happening. All we have are short clips on YouTube showing the army shooting on the city."
Soldiers were said to have opened fire at random in Deraa on Monday, with snipers firing from rooftops and men armed with guns and knives conducting house-to-house searches. Although these reports have not been verified, videos posted online appear to support the claims of witnesses.
Rami Abdul-Rahman of the Syrian Observatory for Human Rights said that arrests also occurred early on Tuesday in the northern coastal city of Jableh. He said phone lines to Deraa were down.
Human rights organisations have warned that the latest crackdown signals an attempt by Syrian regime to deliver a fatal blow to the pro-democracy movement. Syria dismisses that claim, insisting its actions are a response to an Islamist-inspired uprising.
Jordan's powerful Muslim Brotherhood has also condemned the crackdown, denouncing Assad's "violent way" of dealing with protesters. Syria has banned its own Muslim Brotherhood group.