The first members of a U.N. monitoring mission arrived in Syria late Sunday amid hopes from the international community that they could alleviate bloodshed as violence continued to simmer.

Five civilians had been killed by Sunday afternoon, with another five dying of injuries suffered previously, according to the Syrian Observatory for Human Rights. Government officials and rebels accused each other of violating a brittle cease-fire that began Thursday.

Activists reported that government forces fired heavy artillery into areas of the city of Homs dominated by opponents of President Bashar al-Assad. The Local Coordination Committees opposition group reported that shells fell on the Khalidiyah and Qusour neighborhoods of Homs, which has experienced fierce fighting in the 13-month-old uprising against the government.

Syrian officials, meanwhile, asserted that armed rebels were ignoring the cease-fire and continuing to attack security forces. Speaking Saturday, the Syrian ambassador to the United Nations, Bashar al-Jaafari, said that since Syrian authorities agreed on April 1 to implement a peace plan proposed by joint U.N.-Arab League envoy Kofi Annan, there had been an increase in violent attacks by opposition forces.

It was not possible to verify reports from either side because of Syrian restrictions on reporting.

Into this atmosphere of profound mistrust, six unarmed U.N. military observers, who are to be the vanguard of a mission to the Syrian capital of Damascus that could comprise up to 250 people, face a challenging job.

Their role, according to the text of a U.N. Security Council resolution passed Saturday, is to monitor the cessation of violence on all sides and “relevant aspects” of Annan’s six-point peace plan, which includes calls for detainees to be released, humanitarian aid and international journalists to be permitted into the country, and peaceful demonstrations to be allowed.

There is some cause for hope that the U.N. team will go further in its mission than a delegation of monitors from the Arab League did early this year, when it oversaw a lull in violence and wrote a report but produced no lasting results, said Emile Hokayem of the International Institute for Strategic Studies.

“The U.N. has greater experience, so they will be a bit more professional,” he said, but he added that the team may not be equal to the task of quelling violence by a wide range of disorganized rebel factions, as well as a military that has been internationally condemned for its response to the uprising.

“The monitors are going to be stuck in the middle of an extremely murky environment,” Hokayem said. He said Assad’s motivation in accepting the plan, which calls for both sides to cease hostilities, may have been to have the United Nations hold the opposition partially blameworthy for the violence.

The extent to which the monitors would be able to work independently also was called into question Sunday as Syrian officials insisted that they take an active role in the work of the observers.

Government spokeswoman Bouthaina Shaaban told reporters Sunday that the government could not be responsible for the safety of the monitors unless it was involved in “all steps on the ground.” She added that Syria reserved the right to reject observers according to nationality.

Activist groups have expressed mixed feelings about the efficacy of Annan’s initiative to halt the violence. The Local Coordination Committees released a statement Sunday saying that the resolution, “while late, may, in the context of an international role, contribute to reducing the bloodshed of Syrian civilians.”

But an activist outside the city of Hama said demonstrators had been chanting against the presence of U.N. monitors. “We don’t want more people to watch us be killed,” Mousab Alhamadee said via Skype, calling instead for practical help for the opposition, including weapons.