The United Nations was expected Thursday to take up an Arab League proposal that calls for a joint monitoring mission in Syria as President Bashar al-Assad escalated a brutal assault against the opposition calling for an end to his regime.

The move follows what Secretary-General Ban Ki-moon described as a "disastrous" failure this week by the U.N. Security Council to agree on a resolution to condemn the violence in Syria and call for al-Assad to step down.

The fallout from that failed vote is playing out in the streets of the besieged city of Homs - Syria's third-largest city - which has become a flashpoint in the uprising.