Damascus is promising to observe a cease-fire that is scheduled to start early this morning.
However, Syria said it would confront "any assault" by armed groups.
Originally, Damascus was to have pulled out its troops on April as part of a peace plan by the international envoy Kofi Annan and backed by the UN Security Council.
That deadline passed with no withdrawal, and no let-up in the violence.
Activists said at least 12 people were killed on April 11.
Syria's state-run SANA news agency said gunmen killed a senior military official, Jamal Khaled, in a Damascus suburb early in the morning on April 11.
Damascus did not say whether it would pull back its troops, but a spokesman for Annan stressed they should.
Washington is skeptical Syria will keep its word.
U.S. Ambassador to the UN Susan Rice said Syria's pledge holds "little if any credibility."
"Let's be clear what's going on. Fighting is still raging as we speak, reflecting what has been an intensification of the violence that the Syrian government has pursued since April 1 when it committed to cease all hostile actions by yesterday. Its commitments therefore have little if any credibility," Rice said.
In Washington, G8 foreign ministers met to discuss the Syrian crisis. They were expected to urge Russia to pressure President Bashar al-Assad to do more to end the violence.
On a visit to Tehran, Annan urged Iran to help defuse the crisis and warned of "unimaginable consequences" if it escalates.
"If we stick together, support this process, and work with the Syrians, we should be able to find the solution. And I'm grateful for the support of Iran, given its special relations with Syria, and I believe Iran can be part of the solution," Annan said.
Iranian Foreign Minister Ali Akbar Salehi said Assad should be given a chance to make changes and urged no outside interference.
Moscow and Tehran are among Damascus's stronger allies.
The UN says some 9,000 people have died since the uprising erupted more than a year ago.
Based on reporting by AP and Reuters