QAA, Lebanon — Syria accepted a cease-fire drawn up by U.N. envoy Kofi Annan on Tuesday, but the diplomatic breakthrough was swiftly overshadowed by intense clashes between government soldiers and rebels that sent bullets flying into Lebanon.

Opposition members accuse President Bashar Assad of agreeing to the plan to stall for time as his troops make a renewed push to kill off bastions of dissent. And the conflict just keeps getting deadlier: The U.N. said the death toll has grown to more than 9,000, a sobering assessment of a devastating year-old crackdown on the uprising that shows no sign of ending.

Annan’s announcement that Syria had accepted his peace plan was met with deep skepticism.

“We are not sure if it’s political maneuvering or a sincere act,” said Louay Safi, a member of the opposition Syrian National Council. “We have no trust in the current regime. … We have to see that they have stopped killing civilians.”

Annan’s plan calls for an immediate, two-hour halt in fighting every day to allow humanitarian access and medical evacuations. The plan also outlines a complete cease-fire, but that will take more time because Syria must first move troops and equipment out of cities and towns, government forces and the divided opposition must stop fighting, and a U.N.-supervised monitoring mission must b e established.

U.S. Secretary of State Hillary Rodham Clinton said Assad must now act.

“Given Assad’s history of overpromising and under-delivering, that commitment must now be matched by immediate action,” Clinton told reporters in Washington. “We will judge Assad’s sincerity and seriousness by what he does, not by what he says. If he is ready to bring this dark chapter in Syria’s history to a close, he could prove it by immediately ordering regime forces to stop firing and begin withdrawing from populated areas.”

British Foreign Secretary William Hague said Assad’s decision was only a first step.

“We will continue to judge the Syrian regime by its practical actions, not by its often empty words,” he said.

Annan, who is an envoy for the U.N. and the Arab League, has traveled to Russia and China to shore up support for his peace plan. Russia and China have twice shielded Assad from U.N. sanctions over his crackdown, saying the statements were unbalanced and blamed only the government. Syria is Moscow’s last remaining ally in the Middle East and is a major customer for Russia’s arms industry , but the Kremlin has recently shown impatience with Assad.

In Beijing on Tuesday, Annan said China has offered its “full support” for his mission.

In contrast, Iranian President Mahmoud Ahmadinejad offered Assad unequivocal support.

“I’m very happy that Syrian authorities are managing the situation with confidence,” the official Iranian news agency quoted Ahmadinejad as saying. He echoed Assad’s charge that rebels are acting out a Western conspiracy. “Americans want to dominate Syria, Lebanon, Iran and all other countries through the false slogan of defending the freedom of the (Syrian) people, and we must be alert toward their conspiracy,” he said. Iran is one of Syria’s last true allies.

Despite the high-level diplomacy, the situation on the ground remained as bloody as ever.

There were conflicting reports about whether Syrian troops physically crossed the border into Lebanon during heavy fighting near a rural area around the Lebanese village of Qaa.

Two Lebanese security officials told The Associated Press that only bullets whizzed across the frontier.

“There is no Syrian military presence on the Lebanese side of the border,” a military official said, echoing an official denial on the state-run National News Agency, which also said there was no incursion.

But two witnesses in Qaa said they saw dozens of troops enter Lebanon, apparently chasing Syrian rebels. One witness said the Syrian troops burned several homes. Another man showed an AP reporter several high-caliber bullets that he said struck his home.

The witnesses asked not to be identified because of the sensitivity of the matter. An AP reporter at the scene could not verify that any houses were burned, however, as Lebanese soldiers had cordoned off the area. The border in the area is poorly demarcated, and residents cross into each country easily and frequently.

Crackles of gunfire from Syria were clearly heard, even hours after the firefights.

Any movement into Lebanese territory would escalate a conflict that already is spiraling toward civil war. There are concerns the violence could cause a broader conflagration by sucking in neighboring countries.

The Syrian uprising began in March 2011 with mostly peaceful protests as part of the Arab Spring. It turned increasingly militarized after the government unleashed tanks, snipers and troops with machine guns to break up protests — a development that many opposition members say forced them to take up arms. The government denies there is a popular uprising, saying the revolt is being driven by armed groups and others it calls terrorists.

On Tuesday, Assad visited the third-largest city of Homs and its battered neighborhood of Baba Amr, a former opposition stronghold that has become a symbol of the uprising, in what appeared to be a show of his control over even the most rebellious areas.

A monthlong siege by the government to drive rebel fighters out of Baba Amr killed hundreds of people — many of them civilians. Assad’s forces overran the rebel-held district on March 1.

In video shown Syrian state TV, Assad appeared relaxed in a blue shirt and sports coat as he pledged that Baba Amr would return “better than it was before.” He was greeted by residents who shouted, “We are with you until death!”

He met with soldiers and other supporters, shaking hands and embracing women who reached out to him.

The violent conflict has posed a serious challenge to Assad, but neither side has shown any sign of giving in. Assad still has a significant amount of support, particularly from religious minorities and others who feel they could be vulnerable if members of Syria’s Sunni majority — which makes up the backbone of the opposition — take over the country.

Assad and his supporters have played on those fears, suggesting his ouster would spread chaos around the Middle East and leave the country in the hands of extremists.

The opposition, meanwhile, is riven by differences and failed to present a united front against Assad, adding to the chaos.

Opposition leaders met in Istanbul on Tuesday to try to resolve their differences and reassure international backers who are frustrated by the lack of cohesion.

A conference is scheduled for Sunday in Istanbul at which Turkey, the United States and their European and Arab partners will discuss ways to further isolate and pressure Assad, as well as measures to support the Syrian opposition. Some reports indicate that the debate among dozens of countries will include whether the opposition Syrian National Council and affiliated groups should be declared as the sole, legitimate representative of the Syrian people.

On Monday, a Turkish official indicated that a surge of Syrian refugees might compel Turkey, preferably with international backing, to establish a buffer zone on Syrian soil to guarantee the security of its own southern border as well as the welfare of civilians fleeing violence. Turkish officials have long been hesitant to create such a zone.

Establishing a buffer zone on the grounds of Turkish national security would sidestep the gridlock in the U.N. Security Council. But the move would likely lack international consensus, raise questions about Syria’s territorial integrity and highlight a year of failed diplomacy.

AP writers Ayse Wieting in Istanbul, Elizabeth A. Kennedy in Beirut and Ali Akbar Dareini in Tehran contributed to this report.