AMMAN, Jordan—Washington's Arab allies, disappointed with Syria peace talks, have agreed to provide rebels there with more sophisticated weaponry, including shoulder-fired missiles that can take down jets, according to Western and Arab diplomats and opposition figures.

Saudi Arabia has offered to give the opposition for the first time Chinese man-portable air defense systems, or Manpads, and antitank guided missiles from Russia, according to an Arab diplomat and several opposition figures with knowledge of the efforts. Saudi...