With violence reaching new heights in Syria, the United Nations Security Council unanimously approved a 30-day extension of the monitor mission there on Friday, throwing what amounted to a thin lifeline to Kofi Annan, the special envoy in the Syrian conflict, to save his paralyzed peace plan from total irrelevance.

The 15-to-0 vote came only a few hours before the 300-member mission’s authorization was to expire. A failure to act would have forced the monitors into a hasty withdrawal from Syria, just as deadly mayhem, rebel advances and refugee flows from the 17-month-old uprising against the government of President Bashar al-Assad appeared to be accelerating.

Although the work of the monitors has been suspended for more than a month because of the violence and the disregard for Mr. Annan’s plan by both Mr. Assad’s government and his armed opponents, diplomats feared that scrapping the effort entirely would have sent a message of failure at precisely the wrong moment.

“We believe it is the right thing to do, to give a final chance for the mission to fulfill its function,” Britain’s United Nations ambassador, Sir Mark Lyall Grant, told reporters after offering the resolution that was approved.