The main Syrian opposition group estimated that some 1,000 people have been killed in escalating regime attacks in the week leading up to Tuesday's withdrawal deadline, though such figures cannot be verified independently.
France and Britain accused Syria of deception and even Damascus ally Russia seemed critical of Bashar Assad's regime, with Russian Foreign Minister Sergey Lavrov complaining that Syria's "efforts to implement the plan could have been more active and resolute."
Syrian opposition leaders said Tuesday they remain committed to the cease-fire brokered by U.N.-Arab League envoy Kofi Annan, which requires Syrian forces to withdraw from towns and villages on Tuesday and both sides to cease all hostilities by 6 a.m. Thursday.
The truce is widely seen as the last chance for diplomacy, and its collapse could push Syria even closer to an all-out civil war.
The opposition as well as the U.S. and its allies have been deeply skeptical that the regime would comply with the cease-fire because it has violated previous agreements and escalated attacks on opposition strongholds in recent weeks. At the same time, options for ending the fighting appear to be dwindling with the international community unwilling to intervene militarily.
French Foreign Ministry spokesman Bernard Valero on Tuesday dismissed Syria's claims of a withdrawal as "a new expression of this flagrant and unacceptable lie" and British Foreign Secretary William Hague accused Damascus of using the cease-fire deadline "as a cover for intensified military efforts to crush Syria's opposition."
Activists said Tuesday they've seen no signs of a troop pullback.
Instead, regime forces have used heavy weapons including anti-aircraft guns against civilians, Bassma Kodmani, a spokeswoman for the largest opposition group, the Syrian National Council, told reporters in Geneva.
Kodmani estimated that some 1,000 people were killed since Annan announced the cease-fire timeline on April 2. "So every day is a very, very painful time that is given to the Assad regime," she said, adding the death toll was based on figures provided by various groups, including the Syrian Arab Human Rights Network.
Syria restricts the access of foreign journalists, and claims about casualties cannot be verified independently. The U.N. has said previously it believes more than 9,000 people have been killed in the 13-month uprising against Assad.
Annan has not commented on the apparent breakdown of his plan, and his spokesman, Ahmad Fawzi, would only say Tuesday that it's up to the U.N. Security Council to decide what to do next.
As claims and counterclaims about Syrian truce violations flew across the region Tuesday, Annan toured a camp in Turkey, near the Syrian border where hundreds of Syrian refugees greeted him with chants of "Syria, Syria, Syria!"
The Britain-based Syrian Observatory for Human Rights, an activist group, said the Syrian regime gave no indication it was pulling back forces. Instead, the group and activists in Syria reported shelling attacks and raids in several locations in the north, center and south of the country, it said.
"Soldiers are not being withdrawn from towns and villages," said Fadi al-Yassin, an activist in the Idlib province close to Turkey. "On the contrary, reinforcements are being sent."
Associated Press writers Frank Jordans in Geneva, Switzerland, and Vladimir Isachenkov and Nataliya Vasilyeva in Moscow contributed to this report.