DAMASCUS, Syria — The violence in Syria has reached unprecedented levels, the head of the country's U.N. observer mission said Thursday, insisting there must be a cease-fire in order for his teams to resume their work.

About 300 U.N. monitors were sent to Syria to provide an unbiased look at the violence, but they have been confined to their hotels since June 15 because of the bloodshed.

"The escalation of violence, allow me to say, to an unprecedented level, obstructed our ability to observe, verify, report as well as assist in local dialogue," Norwegian Maj. Gen. Robert Mood told reporters in the Syrian capital Damascus.