A team of six U.N. observers set up headquarters in Damascus on Monday and began reaching out to the Syrian government and its opponents in a bid to start healing the country’s divides, even as growing violence jeopardized those plans.

According to a U.N. Security Council resolution passed Saturday, the monitors’ work depends on the continued observance of a cease-fire that went into effect Thursday.

But numerous reports of truce violations by security forces and armed opponents of President Bashar al-Assad, which resulted in the deaths of 12 civilians and an unspecified number of government forces Monday, left the feasibility of the mission in doubt.

The observer team is led by Moroccan Col. Ahmed Himmiche, and 25 more members are expected to arrive in the next few days, said a spokesman for Kofi Annan, the U.N.-Arab League envoy to Syria.

The team is set to monitor the implementation of a six-point peace plan proposed by Annan, accepted by Assad, and backed by Syria’s allies Russia and China as well as Western governments that have called for Assad to step down.

Speaking in New York on Monday, Susan E. Rice, the U.S. ambassador to the United Nations, told reporters, “We are gravely concerned . . . that the violence continues, that the government seems to continue, if not in recent days intensify, bombardment in Homs in particular.”

If the violence continues to escalate, “it will call into question the wisdom and viability of sending in the full monitoring presence,” Rice said, according to news services.

Speaking to reporters in Brussels on Monday, U.N. Secretary-General Ban Ki-moon called the cease-fire fragile but said it was essential that it be maintained so that political dialogue between the government and the opposition could begin.

“Just any small, unintended gunfire may break this fragile process,” Ban said, calling for restraint on all sides.

Peter Harling, an analyst at the International Crisis Group, also expressed concern that there could be a resurgence of attacks by opposition forces and that security forces could use heavy artillery against demonstrators.

“Within the opposition, there’s a lot of concern that this process will only allow the regime to play for time and provide it with room for maneuver in terms of repression on the ground,” he said.

In a recent paper, Harling said both sides in the 13-month-old conflict have become more radicalized, with the escalating violence fueling extremism within the security forces as well as the opposition.

Such hard-liners would be unlikely to abide by a cease-fire, he said, if they thought a political dialogue between Assad’s supporters and opponents was not in their interest.

As of Monday evening, 12 civilians had been killed in fighting in the northwestern province of Idlib, in shelling in Homs and in fighting in the south of the country, according to the Syrian Observatory for Human Rights. Some government forces had been killed as well, but the number was not known. It is difficult to verify claims because the government restricts media access to the country.