Syria's government says it wants "written guarantees" that opposition fighters will stop fighting before it implements a troop pullback agreed by President Bashar al-Assad, but the rebel Free Syria Army has refused the regime demand.
Hours after the government's demand on Sunday, Colonel Riad al-Asaad, a commander of the Free Syria Army told the Associated Press that his group did not recognise Assad's regime and for that reason they would not give guarantees.
He said that if the regime abided by UN-Arab League special envoy Kofi Annan's six-point plan to end the violence, his group would cease fire. He added that the government should withdraw its forces to bases and remove checkpoints from the streets.
Last week, Assad accepted a ceasefire agreement brokered by Annan calling for government forces to withdraw from towns and villages by Tuesday, and for the government and opposition fighters to lay down their arms by 6am local time on Thursday.
In-depth coverage of escalating violence across Syria
But in a statement released on Sunday, Foreign Ministry spokesperson Jihad Makdissi said that earlier reports that Damascus would pull its troops from cities and their suburbs by Tuesday were "wrong", according to the AP.
Makdessi said that Annan had failed so far to submit to the Syrian government "written guarantees regarding the acceptance of armed terrorist groups to halt violence with all its forms and their readiness to lay down weapons".
On Thursday, a UN presidential statement raised the possibility of "further steps'' if Syria did not implement the peace plan outlined by Annan, which Assad agreed to on March 25.
The statement called on all parties, including the opposition, to stop armed violence in all forms in 48 hours after the Syrian government fully fulfills the measures.
The truce is meant to pave the way for negotiations between the government and the opposition over Syria's political future.
Meanwhile, Syrian forces loyal to Assad shelled an area in the province of Idlib near the border with Turkey leaving dozens dead or injured, opposition activists said.
Around 90 tanks and armoured vehicles, backed by helicopters, bombarded the al-Rouge Plain southwest of Idlib city, the provincial capital, activists inside Syria and on the border with Turkey told the Reuters news agency.
Fighters from the Free Syrian Army were surrounded in al-Bashiriya, one of about 40 villages in the plain, activists added.
"The army is shelling al-Rouge with tanks, and helicopters are firing rockets at al-Bashiriya. Tens of people have fallen dead or injured but we cannot get to them because the bombardment is heavy," said activist Mahmoud Ali, with the sound of helicopters audible on the phone, according to Reuters.
Saturday saw some of the deadliest violence yet.
As many as 130 people were killed in an offensive that has sent thousands of refugees surging into Turkey before the UN-backed ceasefire aimed at staunching a year of bloodshed.
On Sunday, the main opposition umbrella group the Syrian National Council called for UN intervention after monitoring groups said 86 of those killed on Saturday were civilians.
Country towns north of Aleppo have endured days of clashes and bombardment, prompting 3,000 civilians to flee over the Turkish border on Friday alone - about 10 times the daily number before Assad accepted Annan's plan 10 days ago.
Recep Tayyip Erdogan, the Turkish prime minister, said on Saturday the number of refugees entering Turkey was rising. Ankara fears an all-out war in Syria would unleash a flood of refugees.
"At the moment we have 24,000 Syrians who have entered Turkey. Of course this number is rising," Erdogan said before departing on a trip to China.
"We are taking measures for this, though we will not close the gates. The United Nations, however, has to toughen its stance," he said.
"In particular Kofi Annan has to hold firm. He announced a deadline of April 10. I believe that he should monitor the situation very closely."
The deaths on Saturday were reported from the cities of Homs, Hama and Aleppo by Syrian opposition groups and Al Jazeera sources.
The town of Taftanaz within the flashpoint province of Idlib also came under attack.
The Local Co-ordination Committees, an activist network, said on Saturday that at least 24 people were killed in the village of al-Latamneh in the suburbs of the city of Hama.
The UK-based Syrian Observatory for Human Rights put the al-Latamneh death toll at 27.
The group said most of those people were killed by shells fired as troops tried to storm al-Latamneh after clashes with defectors there over the past two days.
Farther to the south, at Qusayr in central Homs province, three civilians were killed, including a woman, a child and a defector from the police, said the UK-based activist group.
At least 77 people were killed across Syria on Thursday and 35 on Friday, most of them civilians, according to figures by the Syrian Observatory.
The UN says at least 9,000 people have been killed in Syria since the crisis began 13 months ago.