Syrian troops stormed and shelled districts in a suburb of the capital Damascus Sunday, activists said, a day after the Security Council voted to expand the number of U.N. truce monitors from 30 to 300 in hopes of salvaging an international peace plan marred by continued fighting between the military and rebels.

An eight-member team is already on the ground in Syria, and since Thursday has visited flashpoints of the 13-month-long conflict. Fighting generally temporarily stops when the observers visit an area, but there has been a steady stream of reports of violence from towns and regions where they have not yet gone.

“This U.N. observers thing is a big joke,” said Mohammed Saeed, an activist in the sprawling Damascus suburb of Douma, which came under fire from regime troops on Sunday. “Shelling stops and tanks are hidden when they visit somewhere, and when they leave, shelling resumes.”

His comments reflect a widespread lack of faith among many Syrians in international envoy Kofi Annan’s cease-fire plan for ending the violence in Syria and launching talks between President Bashar Assad and those trying to oust him. Syria’s opposition and its Western supporters suspect Assad is largely paying lip service to the truce since full compliance — including withdrawing troops and heavy weapons from populated areas and allowing peaceful demonstrations — could quickly sweep him from power.

So far, the regime has kept up its attacks on opposition strongholds, though on a smaller scale than before the truce deadline.

Saeed said two people were killed Sunday by indiscriminate firing in Douma, which was the scene of intense clashes between rebels and security forces before the U.N.-brokered cease-fire went into effect more than a week ago.

The Syrian Observatory for Human Rights, a Britain-based opposition group with a network of activists on the ground, confirmed the deaths. It said four soldiers were also killed when a roadside bomb hit an armored personnel carrier in the town later Sunday.

The Observatory also reported that security forces killed three people in the northern province of Idlib and one person in the village of Hteita outside Damascus when troops opened fire from a checkpoint.

It was not immediately clear what prompted the attack on Douma. Saeed said loud explosions that shook the city early Sunday caused panic among residents, some of whom used mosque loudspeakers to urge people to take cover in basements and in lower floors of apartment buildings.

The Security Council approved a resolution Saturday expanding the U.N. observer mission from 30 to 300 members, initially for 90 days. The expanded force is meant to shore up the cease-fire that officially took effect 10 days ago, but has failed to halt the violence that the U.N. says has killed more than 9,000 people since March 2011.

Annan on Sunday welcomed the vote, calling it a “pivotal moment” in the process of stabilizing the country and urged all Syrians to uphold the cease-fire.

“The government in particular must desist from the use of heavy weapons and ... withdraw such weapons and armed units from population centers,” he said.

He added that the presence of observers would help create the conditions conducive to launching the much-needed political process and called on the Syrian government and the opposition “to prepare to engage in such a process as a matter of utmost priority.”

U.N. chief Ban Ki-moon has accused Assad of violating the truce, and said Saturday that “the gross violations of the fundamental rights of the Syrian people must stop at once.” Rebel fighters have also kept up attacks.

State-run news agency SANA said Sunday that an officer was killed and 42 others wounded in a roadside bomb explosion that targeted their bus Sunday in northern Syria. Two other explosives were dismantled on the spot on the Raqqa-Aleppo highway, SANA said.

The U.N. eight-member advance team has visited the Damascus suburb of Arbeen, the southern province of Daraa, and the battered opposition stronghold of Homs. The monitors have not visited Douma yet.

Five monitors who toured Homs Saturday encountered unusually calm streets after weeks of shelling, and activists said it was the first quiet day in months. Two observers stayed behind in Homs to keep monitoring the city, after the rest of the team left that evening.

Amateur video posted on the Internet showed the observers walking through rubble-strewn streets lined by gutted apartments buildings. They were thronged by residents clamoring for foreign military help to oust Assad.

In one video, two monitors are seen sitting in a room listening to a Syrian man asking them to stay in Homs.

“We want you to stay, please stay. ... When you come, shelling stops, killing stops. It’s our blood,” the man says as an observer nods his head.