The Arab League says the Sudanese general who led the group's observer mission to Syria has resigned, as the regional bloc meets in Cairo to consider a new, expanded monitoring team that would include United Nations peacekeepers.

League officials said they accepted General Mohammed Ahmed al-Dabi's resignation Sunday, and nominated former Jordanian Foreign Minister Abdel Elah al-Khatib as the new special envoy for Syria. Al-Khatib was the U.N. troubleshooter for the Libyan crisis last year.

Al-Dabi was harshly criticized for his management of the controversial observer mission, which was perceived by the Syrian opposition to have provided cover for Syria's continued crackdown on an 11-month anti-government uprising.

The 22-member Arab League, which suspended Syria over the violence that has killed thousands, also is considering proposals to expel Syrian ambassadors from Arab capitals and recognize the exiled Syrian National Council. Both moves would help further isolate President Bashar al-Assad.

League officials said they would also call on Syria's disparate opposition groups to unite in order to increase pressure on Mr. Assad's government.

Tunisia's foreign minister told the group his country would host a “Friends of Syria” meeting on February 24, bringing together nations seeking to end the violence in Syria. U.S. and Turkish calls for such a conference followed last week's Russian and Chinese veto of a Western and Arab attempt at the U.N. to pressure Mr. Assad to step down.

On the ground in Syria, activist groups said renewed army shelling killed four civilians Sunday in the flashpoint city of Homs. The opposition Local Coordination Committees said at least 31 people were killed the day before, as Syrian forces backed by tanks and heavy artillery moved in to crush the anti-government revolt.

Meanwhile, al-Qaida chief Ayman al-Zawahri called on Muslims in Iraq, Jordan, Lebanon and Turkey to join the uprising against what he called Mr. Assad's “pernicious, cancerous regime.” All four states border Syria.

Al-Zawahri's comments came a day after two suicide car bombers struck security compounds in Aleppo, a Syrian city that had been relatively peaceful throughout the uprising. While no group has claimed responsibility, suicide bombings are a hallmark of al-Qaida.

Syria's turmoil began with peaceful protests against Mr. Assad's rule, but the revolt has grown increasingly militarized as army defectors and protesters have taken up arms against the government.

In Rome Sunday, Pope Benedict urged the Syrian government to recognize “the legitimate aspirations” of its people and embark on a national dialogue to end the violent crackdown.

The United Nations says violence linked to the uprising has killed more than 5,400 people. But the U.N. said it stopped compiling the death toll in January because it is too difficult to obtain information. Hundreds are reported to have been killed since.