A shaky truce took effect in Syria on Thursday, bringing a respite from the intense bloodshed of recent weeks and prompting the United States to step up pressure for a Security Council resolution that will oblige the Syrian government to fully comply with the terms of a U.N.-brokered peace plan.

But with both sides to the conflict exchanging allegations of violations and no indication that Syrian security forces were preparing to relax their stranglehold on opposition flash points, there was skepticism about whether the lull would last.

Activist groups said at least five people were killed when Syrian troops opened fire on demonstrators and on civilians returning to their homes, and President Bashar al-Assad's government accused “terrorists” of carrying out two bombings and an assassination in which at least two people died.

It was clear, however, that Syria was quieter than it has been for months, leading to cautious hope that the six-point peace plan proposed by the joint U.N.-Arab League envoy Kofi Annan may help end the bloodshed and usher in a negotiated settlement to the country’s 13-month-old uprising.

“Syria is apparently experiencing a rare moment of calm on the ground,” Annan said in a statement from Geneva. “This must now be sustained.”

In Washington, Secretary of State Hillary Rodham Clinton cautioned that the cease-fire could be considered only “a fragile first step.”

“Sporadic fighting continues in parts of Syria,” she told reporters at a Group of Eight meeting. Assad's forces “have not pulled back, and he has not taken any action on any of the other points.”

The United States is now pushing for a speedy resolution at the United Nations that would oblige Assad to comply with all the requirements of the six-point plan, including the withdrawal of troops from cities, access for humanitarian aid and journalists, and permitting peaceful protests, she said.

“The Annan plan is not a menu of options,” Clinton said. “They cannot pick and choose.”

The United States circulated a draft resolution at the United Nations that would establish an advance team of up to 30 U.N. monitors to observe the cease-fire. The council is expected to follow up in the coming weeks with a second resolution that would establish a full-fledged monitoring mission with as many as 250 monitors, most of them recruited from other U.N. missions in the region.

There was broad consensus in the 15-nation Security Council about the need to support Annan’s request for U.N. monitors, and Russia’s U.N. envoy, Vitaly Churkin, said it was possible the council could approve the mission by Friday.

Whether the lull in violence signaled any more than a pause was in question. The sustained shelling of residential areas loyal to the opposition that had killed hundreds of people in recent weeks came to a halt, but there was no indication that the government had pulled its forces out of the cities.

Such a move could trigger a revival of the mass demonstrations that shook the country in the early months of the uprising, and the government appeared intent on preventing the opposition from taking advantage of the cease-fire to call people onto the streets.

At least two of those killed Thursday were displaced civilians who tried to take advantage of the cease-fire to return to their homes in neighborhoods of the restive city of Homs but were shot by snipers, said Abu Rami, an activist with the Syrian Revolution General Commission, who is in Homs.

“This was a special day, because it was the first day of the cease-fire, so people had some confidence and they tried to go out in the streets and go back to what was left of their homes,” he said. “But these snipers on the roofs had no mercy and they shot them.”

The biggest test of the cease-fire will come Friday, when Syrians routinely take to the streets to stage protests, and the security forces typically respond by opening fire to disperse them.

The signs on Thursday were not encouraging; troops reportedly opened fire on demonstrators who sought to take advantage of the trucein several locations around the country, including Hama, Idlib, Deir al-Zour and the Damascus suburb of Qaboun, where a man was shot dead, according to the opposition Local Coordination Committees. The group said a total of 22 people were killed in different incidents of violence, but the figures could not be independently verified.

Salman Shaikh, director of the Brookings Doha Center in Qatar, said the Syrian government would have to do more to comply with all the terms of the peace plan if the cease-fire were to be considered a success. “This kind of partial implementation with this menacing climate can’t last for long,” he said.

The Syrian news agency SANA also accused the opposition of continuing to carry out attacks. An army first lieutenant was killed and 24 members of the security forces were injured when a bomb targeted their bus on a highway outside Aleppo, SANA reported. In addition, an unspecified number of security force members were killed and injured in an explosion in Idlib, and a local member of the ruling Baath Party was assassinated as he drove his car in the southern province of Daraa, the news agency said.

Still, Annan, who briefed the Security Council in a closed-door video-conference, indicated that the pause in fighting provides an opportunity to get a U.N. mission into the country to help reinforce the cease-fire and to lead to the implementation of the other elements of the peace plan.

Norwegian Maj. Gen. Robert Mood was in Damascus recently planning the terms of a monitoring mission, and U.N. Secretary General Ban Ki-moon said Mood may return to Damascus as early as Friday.

An Arab League monitoring mission in January was judged a failure because it was overly reliant on the Syrian security forces for access to opposition strongholds, its members were not trained and they lacked any form of protection against the violence raging in many of the areas they were expected to visit.

Lynch reported from the United Nations. Staff writer Karen DeYoung in Washington and correspondent Alice Fordham in Beirut contributed to this report.