United Nations monitors in Syria have suspended operations because of the increasing violence over the last 10 days, the head of the observer mission said.

"The observers will not be conducting patrols and will stay in their locations until further notice," General Robert Mood said in a statement.

"There has been an intensification of armed violence across Syria over the past 10 days," the mission chief said.

"This escalation is limiting our ability to observe, verify, report as well as assist in local dialogue and stability projects - basically impeding our ability to carry out our mandate.

"The lack of willingness by the parties to seek a peaceful transition, and the push towards advancing military positions is increasing the losses on both sides: innocent civilians, men women and children are being killed every day.

"It is also posing significant risks to our observers.

"In this high risk situation, UNSMIS [United Nations Supervision Mission in Syria] is suspending its activities," Gen Mood said.

The observers will not conduct patrols and will stay in their locations until further notice," he said, adding that "engagement with the parties will be restricted."

Gen Mood said the suspension will be reviewed on a daily basis, and that "operations will resume when we see the situation fit for us to carry out our mandated activities."

"Let me be very clear, UNSMIS is committed to the people of Syria. We stand ready to work with all parties to assist in bringing an end to the violence and promote political dialogue. A return to normal operations remains our objective."

Gen Mood had already said that the escalating bloodshed was hampering the ability of observers to carry out their duties.

Separately, the US State Department said this afternoon that the sooner a political transition occurs in Syria the higher the odds of preventing a long and bloody civil war.

"We are consulting with our international partners regarding next steps toward a Syrian-led political transition as called for in Security Council Resolutions 2042 and 2043," it said in a statement.

It echoed one issued by the White House after the suspension of a UN monitoring mission's activities in Syria.

"The sooner this transition takes place, the greater the chance of averting a lengthy and bloody sectarian civil war," the State Department spokeswoman added in the statement.