(CBS/AP) BEIRUT - A U.N.-brokered plan to stop the bloodshed in Syria effectively collapsed Sunday after President Bashar Assad's government raised new, last-minute demands that were swiftly rejected by the country's largest rebel group.
Syria demanded "written guarantees" Sunday that its opponents will lay down their weapons before the government withdraws troops from cities, derailing a U.N.-brokered truce that was supposed to start in two days.
The truce plan, devised by U.N.-Arab League envoy Kofi Annan, was supposed to go into effect on Tuesday, with a withdrawal of Syrian forces from population centers, followed within 48 hours by a cease-fire by both sides in the uprising against four decades of repressive rule by the Assad family.
But on Sunday, Syria's Foreign Ministry said that ahead of any troop pullback, the government needs written guarantees from opposition fighters that they will lay down their weapons.
The commander of the rebel Free Syrian Army, Riad al-Asaad, said that while his group is ready to abide by a truce, it does not recognize the regime "and for that reason we will not give guarantees."
Annan's spokesman had no comment on the setback. The envoy has not said what would happen if his deadlines were ignored.
Even before the setback, expectations were low that the Assad regime would honor the agreement.
Russia, an Assad ally that supports the cease-fire plan, may now be the only one able to salvage it. The rest of the international community, unwilling to contemplate military intervention, has little leverage over Syria.
In recent days, instead of preparing for a withdrawal, regime troops have stepped up shelling attacks on residential areas, killing dozens of civilians every day in what the opposition described as a frenzied rush to gain ground. Activists said at least 21 people were killed in violence on Sunday and as many as 40.
"Mortar rounds are falling like rain," said activist Tarek Badrakhan, describing an assault in the central city of Homs on Sunday. He spoke via Skype as explosions were heard in the background. The regime is exploiting the truce plan "to kill and commit massacres," he said.
Just as Annan complained Sunday that the escalation was "unacceptable," Syria said its acceptance of the Annan deal last week was misunderstood and suggested it would not be able to withdraw its troops under current conditions.
In addition to demanding written guarantees from the opposition, Foreign Ministry spokesman Jihad Makdessi said Syria also wants assurances from Annan that Qatar, Turkey and Saudi Arabia -- Assad's most active critics -- halt "financing and arming of terrorist groups."
Qatar and Saudi Arabia are said to be creating a multimillion dollar fund to pay rebel fighters, while Turkey has floated the idea of creating buffer zones for refugees in Syrian territory, near the Turkish border.
Many had expected the Assad regime to stall and create new obstacles to a truce because it has little to fear from the international community, said Peter Harling, an analyst at the International Crisis Group think tank.
"Nothing seems to have a price tag," he said, noting that regime has been accused of shelling whole neighborhoods, exacting collective punishment and driving people out of their homes.
The regime might also be reluctant to move forward for fear of losing control.