Rebels in Syria have rejected a last-minute demand by the government, made just 48 hours ahead of a proposed ceasefire which now looks set to fail.
The rebels' commander says they will abide by the UN-Arab League truce, but will not deal directly with Damascus while troops continue their assault.
The government on Sunday called for written guarantees from rebels to end attacks and a promise from foreign states not to fund them.
Violence has spiked ahead of the deal.
Activists said nearly 70 people were killed on Sunday, bringing the weekend death toll over the weekend to at least 180, most of them civilians.
Syria's opposition say the new demands are a ploy by President Bashar al-Assad to derail the peace plan.
'Committed to plan'
The Free Syrian Army's Col Riyad al-Asaad told the Agence France-Presse news agency that his troops were "committed" to the plan, which was mediated by UN-Arab League envoy Kofi Annan.
"We will present our guarantees and our commitments to the international community, but not to this (Syrian) regime."
The ceasefire is due to come into effect on Tuesday after government troops pull back from populated areas.
But on Sunday, the Syrian foreign ministry cast new doubt on the agreement, saying it did not want the rebels to exploit any troop withdrawal to reorganise and rearm themselves.
"To say that Syria will pull back its forces from towns on April 10 is inaccurate, Kofi Annan having not yet presented written guarantees on the acceptance by armed terrorist groups of a halt to all violence."
It said that the regime was also awaiting written guarantees from the governments of Qatar, Saudi Arabia and Turkey "on stopping their funding to terrorist groups".
"Syria is not going to repeat what happened in the presence of Arab observers when armed forces left towns," the foreign ministry said, referring to a monitoring mission by the Arab League earlier this year which failed to end the violence.
Foreign ministry spokesman Jihad Makdissi said: "Syria has a plan for military pullback already in place and being implemented, but completing and achieving the main goal would definitely require the guarantees from the other side and those supporting them."
Meanwhile, Mr Annan called the recent escalation of violence "unacceptable" and appealed to the Syrian government to abide by its commitments.
"This is a time when we must all urgently work towards a full cessation of hostilities, providing the space for humanitarian access and creating the conditions for a political process," he said.
More than 9,000 people have been killed in the uprising against Mr Assad's rule which began more than a year ago.