BEIRUT (AP) -- Syria promised to stop fighting in time for Thursday's deadline for a cease-fire brokered by special envoy Kofi Annan but reserved the right to respond to any aggression, a significant hedge against any end in the fighting that has convulsed the nation for more than a year.

The statement came Wednesday as Annan was in Tehran to seek support for his faltering plan to stop the country's slide toward civil war. Iran is one of Syria's most powerful allies.

Many world leaders see Annan's plan -- which called for Syria to pull its tanks back to barracks on Tuesday, followed by a full cease-fire by both sides by 6 a.m. Thursday -- as the best hope to calm a year-old conflict that has killed 9,000 people.

But the U.S. and others also are skeptical President Bashar Assad's regime will fully comply after several previous failures. Syria disregarded the Tuesday deadline, and was still attacking its opponents Wednesday with rockets and mortar fire.

In a statement carried on the state-run SANA news agency, a defense official said Syria's army successfully fought off "armed terrorist groups,'' which is the term Damascus uses to describe those behind the country's year-old uprising.

"A decision has been taken to stop these missions as of the morning of Thursday, April 12, 2012,'' the unnamed official said, adding: "Our armed forces are ready to repulse any aggression carried out by the armed terrorist groups against civilians or troops.''

The U.N. has ruled out any military intervention of the type that helped bring down Libya's Moammar Gadhafi, and several rounds of sanctions and other attempts to isolate Assad have done little to stop the bloodshed.

The Syrian uprising is among the most explosive of the Arab Spring, and the U.N. estimates 9,000 people have been killed in the conflict since March of last year.

The presence of Syrian tanks, along with security forces and snipers, have largely succeeded in preventing protesters from recreating the fervor of Egypt's Tahrir Square, where hundreds of thousands of people camped out in a powerful show of dissent that ultimately drove longtime leader Hosni Mubarak from power.

It's not clear how Syria can fully abide by Annan's plan without risking an embarrassing -- and potentially dangerous -- Tahrir-style sit-in, or losing control over territory that government forces recently recovered from rebels.