Thousands of Syrian refugees have been fleeing into Turkey, officials there say, as UN chief Ban Ki-moon warns the crisis is escalating.
More than 2,300 fled on Wednesday, by far the highest number in one day.
Earlier, the UN called for the Syrian government to "urgently" implement an agreed ceasefire.
The approach of the deadline for a ceasefire seems to have brought an intensification rather than reduction in violence.
In the Jouret al-Shiyah quarter of Homs, shells or rockets were falling at a rate of four in 30 seconds.
Activists accuse the government of trying to complete its crackdown come what may; government officials say it is the rebel fighters who are exploiting the impending withdrawal of the military from towns and cities to improve their position.
Activist groups say at least 60 people were killed in shelling or shooting by security forces on Thursday in various parts of the country, mainly the central city of Homs and Idlib province in the north-west.
Syrian President Bashar al-Assad, who is fighting to crush a year-long uprising, agreed late last month to a UN-Arab League peace plan which sets a 10 April deadline for a ceasefire.
A UN team has arrived in Damascus to negotiate the possibility of deploying UN monitors to oversee any ceasefire.
The BBC's Jim Muir, reporting from Beirut, says the real test of the commitment of both sides to the ceasefire will come on Tuesday, by which time the government has pledged to stop using heavy weapons and to pull troops and tanks out of population centres.
If that happens, our correspondent says, the opposition side will be under strong pressure to follow suit and call off all armed attacks.
A Turkish official told Reuters news agency that the refugees crossed near to the Turkish village of Bukulmez and that others were waiting on the other side of the border.
The new arrivals were taken to a refugee camp in Reyhanli in 44 minibuses, he said.
More than 42,000 Syrians have fled the country since the beginning of the revolt, which the UN estimates has killed more than 9,000 people.
The Syrian authorities say about 2,000 security personnel have also been killed.
Turkish Prime Minister Recep Tayyip Erdogan said on Thursday he did not trust President Assad to comply with the peace plan.
"He shoots people but pretends he is withdrawing troops. He is not withdrawing troops but he is duping the international community."
Earlier, Mr Ban said the violence was claiming lives every day and appealed to Mr Assad "to show vision and leadership".
"Cities, towns and villages have been turned into war zones. The sources of violence are proliferating," Mr Ban told the UN General Assembly. "The human rights of the Syrian people continue to be violated… Humanitarian needs are growing dramatically."
'Protection of civilians'
UN and Arab League envoy Kofi Annan's plan calls for Damascus to pull back troops and heavy weaponry by 10 April, and for a full ceasefire to take hold within another 48 hours.
Mr Annan, the former head of the UN, said he expected a full ceasefire to take effect by 06:00 (03:00 GMT) on 12 April.
But Syria's UN ambassador said that the main threat to the ceasefire came from the armed opposition backed by Qatar, Saudi Arabia and Turkey.
Bashar Jaafari demanded that Mr Annan obtain written guarantees from those countries that they were on board with the peace plan.
He also said that while troops and heavy weapons would be withdrawn from cities under the plan, police would remain "for the protection of the civilians".
Mr Annan is expected to travel to Iran on 11 April, the day after the partial ceasefire is due, to try to win further regional support for his peace plan.
The UN has requested that Mr Annan provide proposals for a mechanism to supervise the ceasefire to and update the Security Council on progress.
Mr Annan said that if the ceasefire was successful a small mobile UN monitoring mission of some 200-250 observers could be brought into Syria.