CAIRO — The Arab League asked the United Nations Security Council on Sunday to send a peacekeeping mission to Syria, and it called on Arab nations to sever diplomatic relations with Damascus in an effort to pressure the government to end the violence there.

At a meeting of foreign ministers in Cairo, the league grasped for new ways to end a conflict that appeared to be escalating into a civil war. The league’s observer mission to Syria failed to end the bloodshed last month.

The ministers adopted a resolution asking the Security Council to authorize a joint Arab-United Nations force to “supervise the execution of a cease-fire,” and it urged the league’s members to “halt all forms of diplomatic cooperation” with the Syrian government.

The resolution said that the league supported “opening channels of communication with the Syrian opposition and providing all forms of political and financial support to it,” although it did not specify what that support would be, nor did it recognize the Syrian National Council, an umbrella opposition group, as the legitimate representative of the Syrian people.