Updated at 3:07 p.m. ET

(CBS/AP) UNITED NATIONS – Russia and China again vetoed a Western-backed U.N. resolution Thursday aimed at pressuring President Bashar Assad’s government to end the escalating 16-month conflict in Syria.

The 11-2 vote, 사설 토토 검증 with two abstentions from South Africa and Pakistan, was the third double veto of a resolution addressing the Syria crisis by Damascus’ most important allies.

The defeat leaves in limbo the future of the 300-strong U.N. observer mission in Syria, which was forced to suspend operations because of the intensified fighting. Its mandate, to monitor a cease-fire and implementation of international envoy Kofi Annan’s peace plan, expires Friday.