The head of the Arab League's observer mission to Syria has resigned, a league official said Sunday. 

The news of Sudanese Gen. Mohammed Ahmed Al-Dabi's resignation came on the same day that foreign ministers from the 22-member group were to consider a proposal to send a new mission to Syria with Arab League and UN observers.

The official said League chief Nabil Elaraby will nominate former Jordanian Foreign Minister Abdul-Illah al-Khatib as the new envoy to Syria. The official spoke on condition of anonymity because of the sensitivity of the subject.

Also Sunday, U.S. President Barack Obama's chief of staff spoke bluntly about the government of President Bashar Assad, saying it is only a matter of time before it collapses.

"There is no question that this regime will come to an end. The only question is when," Jacob Lew told Fox News.

Lew said the "brutality of the Assad regime" is unacceptable and has to end," while adding that that the Syrian people "have to handle this in a way that works in Syria."

The Arab League suspended its observer mission last month amid a surge in violence as Assad's regime battles an uprising that began 11 months ago.

'There is no question that this regime will come to an end. The only question is when.'—Jacob Lew, U.S. president's chief of staff

The proposal was to be discussed in a meeting in Cairo by a "Syria Group" made up of seven member states led by Qatar, according to the officials. The group would make recommendations to an Arab League foreign ministers' meeting scheduled for later Sunday in the Egyptian capital.

Last month, the League pulled out its observer mission to Syria after it came under heavy criticism for failing to stop the bloodshed engulfing the country. The Syrians would be unlikely to accept a new observer team.

Call for Syrian opposition groups to unite

The UN estimates that 5,400 people have been killed since March, but that figure is from January, when the world body stopped counting because the chaos in Syria has made it all but impossible to check the figures. Hundreds are reported to have been killed since.

The League officials, speaking on condition of anonymity because the proposals had not yet been adopted, said the Syria Group would also call on Syrian opposition groups to close ranks and unite under one umbrella, a move that they said would place more pressure on the Assad regime.

The Syria Group meeting would be preceded by talks in Cairo by the foreign ministers of the Gulf Cooperation Council, a regional grouping that brings together Saudi Arabia, Kuwait, Qatar, United Arab Emirates, Oman and Bahrain.

The six nations, particularly Saudi Arabia and Qatar, have been campaigning for a tougher stand against Assad's regime and may in their Cairo meeting offer formal recognition of Syria's National Syrian Council, the largest of Syria's opposition groups.

UN resolution vetoed

Syria's turmoil began with peaceful protests against Assad's rule, sparking the fierce regime crackdown. But the revolt has grown increasingly militarized as army defectors and armed protesters have taken up arms against the government.

Russia and China last weekend vetoed a Western and Arab resolution at the UN that would have pressured Assad to step down. The draft resolution demands that Assad halt the crackdown and implement an Arab League peace plan that calls for him to hand over power to his vice-president and allow creation of a unity government to clear the way for elections.

The veto prompted Western and Arab countries to consider forming a coalition to help Syria's opposition, though so far there is no sign they intend to give direct aid to the Free Syrian Army.

Damascus allowed in Arab League observers in December, but the mission was halted amid the accelerating bloodshed. The Syrians would be unlikely to accept a new observer team.