TEHRAN, Iran - Syria promised to comply with a UN-brokered cease-fire beginning Thursday but carved out an important condition -- that the regime still has a right to defend itself against the terrorists that it says are behind the country's year-old uprising.

The statement Wednesday offered a glimmer of hope that a peace initiative by special envoy Kofi Annan could help calm the conflict, which has killed some 9,000 people. But the regime still has ample room to manoeuvr.

In comments carried on the state-run news agency, Syria said the army has successfully fought off "armed terrorist groups" and reasserted state authority across the country.

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

The government denies that it is facing an uprising by Syrians who want to dislodge the authoritarian family dynasty that has ruled the country for more than four decades. Instead, the regime says, terrorists are carrying out a foreign conspiracy to destroy Syria.

Because the regime has treated any sign of dissent as a provocation, there are only dim hopes for an abrupt end to the bloodshed.

The White House cautioned that President Bashar Assad's regime has reneged on promises to stop the violence in the past.

"What is important to remember is that we judge the Assad's regime by its actions and not by their promises, because their promises have proven so frequently in the past to be empty," White House spokesman Jay Carney told reporters in Washington.

Annan is scheduled to brief the UN Security Council on Thursday by videoconference from Geneva.

Many activists predict that huge numbers of protesters would flood the streets if Assad fully complies with the agreement and pulls his forces back to barracks. But Syria has ways to maintain authority even without the military, in the form of pro-regime gunmen called "shabiha" and the fiercely loyal and pervasive security apparatus.

Over the course of the uprising, the military crackdown succeeded in preventing protesters from recreating the fervour of Egypt's Tahrir Square, where hundreds of thousands of people camped out in a powerful show of dissent that drove longtime leader Hosni Mubarak from power.

In the early days of the Syrian rebellion, Syrian forces used tanks, snipers and machine-guns on peaceful protesters, driving many of them to take up arms. Since then, the uprising has transformed into an armed insurgency. Many fear the conflict could soon become a civil war.

The rebel Free Syrian Army, a fighting force determined to bring down Assad, has said it will abide by the cease-fire Thursday. But the opposition is not well organized, and there are growing fears of groups looking to exploit the chaos.

Annan said Wednesday that he is hopeful both sides will abide by their agreement.

"We've been in touch with them (Syrian rebels) and have had positive answers from them," Annan said, speaking on a visit to Iran. "We should see a much improved situation on the ground."

Western powers have pinned their hopes on Annan's plan, in part because they are running out of options. The UN 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 West or Arab states have very little leverage over Syria, and the one thing which would certainly weaken the regime -- which is some form of military intervention -- is the one policy that is not being considered," said David Hartwell, senior Middle East analyst at the defence and intelligence group IHS Jane's.

Saudi Arabia and Qatar have called for arming the rebels, but even if they follow through there is no guarantee that such efforts could cripple Assad's well-armed regime.

Asked what steps the U.S. could take if the deal collapses, Carney, the White House spokesman, cited humanitarian and other non-lethal assistance and further sanctions.

The conflict is among the most explosive of the Arab Spring, in part because of Syria's web of allegiances to powerful forces including Lebanon's Hezbollah and Shiite powerhouse Iran.

Annan's peace plan called for Syria to withdraw its forces on Tuesday, followed by a full cease-fire by 6 a.m. Thursday. The halt in fighting would then pave the way for an observer mission and talks between both sides over the country's future.

Syria disregarded the Tuesday deadline and was still attacking its opponents Wednesday with tanks and mortar fire. The government has escalated military attacks in recent weeks, prompting accusations that Assad was using the peace plan as cover for more violence.

It was unclear if Wednesday's promise to comply with the truce meant Syria would pull back its troops or just stop its offensives.

But Annan welcomed it and said he will work with the Syrian government to implement his six-point plan to end the bloodshed.

"The joint special envoy looks forward to the continue support of relevant countries in this regard," said Annan's spokesman, Ahmad Fawzi.

Annan was in Iran -- Syria's key regional ally -- to press for support for his peace plan.

"Iran, given its special relations with Syria, can be part of the solution," Annan said during a news conference in Tehran. "The geopolitical location of Syria is such that any miscalculation and error can have unimaginable consequences."

Annan earlier secured the backing of Russia and China, which have given Assad a significant layer of protection by blocking strong action against the regime at the UN Security Council. Those two countries fear a resolution condemning Assad might open the door to possible NATO airstrikes on Syria, recalling the military campaign in Libya.

Despite Wednesday's diplomatic push, activists reported more violence.

Activists said the central city of Homs was under siege.

Tarek Badrakhan, a resident of Homs, said the regime has been shelling restive areas for weeks, including the rebel-held neighbourhood of Khaldiyeh.

"This city of Homs is a ghost city today and Khaldiyeh in particular is mostly destroyed," he told The Associated Press. "We are being subjected to intense shelling. Yesterday and today were the worst days. Reconnaissance planes are flying overhead to locate targets."

The wounded were being treated inside homes after a makeshift hospital was destroyed earlier this week. Dozens of corpses that were being kept inside the clinic had to be buried in a public garden, he said.

The Britain-based Syrian Observatory for Human Rights activist group reported clashes in the Barada Valley region on the outskirts of Damascus between troops and army defectors as government forces stormed the area. The Observatory said dozens of people were wounded.

Activist Fares Mohammed said two people were killed there.

"Many of the wounded lost limbs as a result of shelling by tanks," he said.

Syrian state-run news agency SANA said gunmen shot and killed army Brig. Gen. Jamal Khaled in the Damascus suburb of Aqraba on Wednesday morning. It added that Khaled's driver, a soldier, was also killed in the attack.

Bassam Imadi, a member of the opposition Syrian National Council, said he had no faith in the Annan initiative to stop the bloodshed.

"Peace will never come to this country before this regime is overthrown -- that is something for sure," Imadi said. "The regime is using all these breaks, those initiatives, those diplomatic and political solutions only to try and finish the uprising."