BEIRUT — Syrian government forces appeared Thursday largely to have ended their attacks on anti-government strongholds, adhering to a United Nations-brokered cease-fire.

But the United States, France and others seeking the ouster of Syrian President Bashar Assad said the government has yet to implement a provision in the U.N. plan that called for the country's military to return to its barracks, and the U.S. repeated calls for Assad to step down.

Anti-Assad activists reported at least three deaths at the hands of Syrian security forces on Thursday, along with a number of arrests.

The official Syrian government news service, SANA, reported at least two government sympathizers killed — a police officer who died when the bus he was in was bombed near the city of Aleppo, wounding 24 others, and a Baath party official in southern Daraa province who was shot eight times when he left his home to buy bread. SANA said 14 members of the security services, killed in previous violence, were buried.

President Barack Obama and French President Nicolas Sarkovy held a video conference, after which the White House said the two leaders had "condemned the violence perpetrated by the (Assad) regime against its own people and noted that the regime had yet to fully implement the agreement."

U.S. Secretary of State Hillary Clinton welcomed the "apparent halt in violence," but she said it was not enough. "If it holds, a cease-fire is an important step, but it represents just one element of the special envoy's plan," she said. "Assad will have to go and the Syrian people must be given the chance to chart their own future."

U.N. Syria envoy Kofi Annan, the author of the cease-fire plan, made no public statement. In a private briefing to the Security Council, he reportedly called for approval of envoys to monitor the cease-fire's progress. U.N. Secretary-General Ban Ki-moon, in Geneva, said that without monitors "it was difficult to assess the situation on the ground."

"Even a small gunshot may give both sides the pretext to engage in another fighting," Ban said, according to the Associated Press.

What happens next is difficult to predict. The Syrian government warned Wednesday that it would respond with force to any attack by members of the Free Syrian Army, the name taken by the loosely organized and lightly armed army defectors and volunteers who took up arms against Assad's government, and activists said they hoped for widespread demonstrations on Friday after weekly prayer services.

The Annan plan also calls for the Assad government and its opposition to begin talks based on finding a peaceful solution to the country's impasse, but it was unclear what the mechanism for such talks would be or who would take part. The Syrian National Council, led largely by longtime Syrian exiles, remains divided over how to proceed.

The Syrian government also has promised to allow foreign journalists to enter the country, allow humanitarian aid to be delivered in conflicted areas, and permit anti-government demonstrations.

"The Annan plan is not a menu of options. It is a set of obligations," Clinton said. "The burden of fully and visibly meeting all of these obligations continues to rest with the regime. They cannot pick and choose."

The cities of Homs and Hama in central Syria remained the most volatile as the cease-fire went into effect at 6 a.m., with anti-government activists reporting a few instances of shelling and some light arms fire. Activists said Syrian soldiers executed a man at a checkpoint in a village outside Hama, and that two other people died when the Syrian military fired at a demonstration in the northern city of Idlib. Some activist groups reported as many as 18 total deaths across the country.