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.
Damascus on Sunday called for written guarantees from rebel fighters to end attacks and a promise from foreign states not to fund them.
The Free Syrian Army said it backed the UN-Arab League truce, but refused to meet the government's demands.
Violence has risen ahead of Tuesday's deadline for the ceasefire to start.
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.
On Monday, Turkey said a Turkish translator and two Syrian nationals were wounded overnight at the Kilis refugee camp by shots fired from the Syrian side of the border.
Also on Monday, Syrian Foreign Minister Walid Muallem is visiting Russia - Syria's key ally - for what may now be crucial talks on the crisis.
Syria's opposition says the new demands are a ploy by President Bashar al-Assad to derail the peace plan mediated by UN-Arab League envoy Kofi Annan.
The Free Syrian Army's Col Riyad al-Asaad told Associated Press news agency that while his troops were "committed" to the plan, they did not recognise the Assad government "and for that reason we will not give guarantees".
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.
The shooting into the Kilis refugee camp is the first such attack since Turkey began housing refugees. Turkey called in the Syrian charge d'affaires to protest.
Mr Annan will reportedly visit Syrian refugees on the Turkish border on Tuesday.
A Turkish diplomatic source told AFP: "The visit will only last a few hours, ahead of Annan's trip to Iran."
The BBC's Jonathan Head, on the Turkey-Syria border, says this is a necessary move by Kofi Annan as there is a diplomatic need for him to show his concern for those who have fled.
Mr Muallem is scheduled to travel to Moscow on Monday for talks and correspondents say the focus may now fall on Russia to try to salvage the Annan plan.
On Monday Chinese foreign ministry spokesman Liu Weimin called on the government and opposition in Syria to "honour their commitment of ceasefire and withdrawal of troops".
However, the violence showed no sign of abating on Monday, with the Syrian Observatory for Human Rights group reporting that at least six members of the Syrian security forces had been killed in clashes close to the Turkish border.
The UN says more than 9,000 people have been killed in the uprising against Mr Assad's rule which began more than a year ago.
The Syrian government says 2,000 security personnel have been killed in the uprising and blames the violence on "armed gangs" and "terrorists".