Saudi Arabia recalled its envoy to Syria in a major escalation of international pressure Monday after security forces killed more than 50 people and the regime defended its crackdown on "outlaws."

The shock move by Riyadh, the Middle East's Sunni Muslim heavyweight, followed condemnation by Pope Benedict XVI and the Arab League over the continuing bloodshed.

The U.S. envoy to Syria has returned to monitor the "grotesque" crackdown there, placing himself on a collision course with Damascus, which has imposed strict constraints on diplomats.

Washington on Thursday sent Ambassador Robert Ford back to Syria, where President Bashar al-Assad's troops and tanks have stormed major cities in an effort to suppress a months-long pro-democracy revolt.

Jordan said on Sunday the bloody crackdown on the opposition in Syria is "worrisome," and called for dialogue and reforms to end the crisis in the neighboring country.

"What is happening in Syria now is worrisome, unfortunate and sad," Foreign Minister Nasser Judeh told the state-run Petra news agency in an interview.

Kuwait, which has called for a halt to bloodshed in Syria, said on Sunday it has no plans to expel the Syrian ambassador as demanded by MPs and protesters.

"The Syrian ambassador is here and he will stay in accordance with diplomatic agreements," foreign ministry undersecretary Khaled al-Jarallah told reporters.

Rebels in the western Libyan town of Zliten were said to be low on ammunition and on the defensive on Sunday, as the regime said its forces had retaken the strategic southwest town of Bir Ghanam.

Abdul Wahab Melitan, a rebel spokesman in the port city of Misrata near Zliten, said forces loyal to strongman Moammar Gadhafi had launched an assault on rebel positions in Zliten's Souk Telat area, killing three and wounding 15.

The Arab League on Sunday called on the Syrian authorities to "immediately" stop the violence that has rocked the country since mid-March, in the pan-Arab body's first official statement on the unrest.

League Secretary General Nabil al-Arabi "calls on the Syrian authorities to bring an end immediately to acts of violence and campaigns by the security forces against civilians," the statement said.

Bahrain has ordered the release of two former MPs arrested in May after a crackdown on Shiite-led protests pending their trial in a civilian court, state news agency BNA said on Sunday.

The public prosecutor has decided to "release several detainees ... until the (civilian) court looks into their cases," including "two former MPs and a lawyer," BNA reported.

Syrian forces backed by tanks killed at least 57 people on Sunday in the regions of Deir Ezzor, Homs and Idlib, activists said, as President Bashar al-Assad defended what he termed the state's duty to crack down on "outlaws" despite mounting condemnation.

Security forces killed at least 38 civilians in the city of Deir Ezzor alone, activists said, and at least seven more died in Hula, a town in Homs province, in a separate assault with tanks.

Syria’s foreign ministry on Sunday rejected criticism from the Gulf Cooperation Council of Damascus’ violent crackdown on protests and called for Gulf states to instead condemn "the violence of armed groups” and to “allow time for the reforms" proposed by President Bashar al-Assad.

“Syria has received with regret the statement of the Gulf Cooperation Council (GCC), which completely ignored the information and facts presented by Syria on the killing and sabotage acts committed by armed terrorist groups seeking to undermine the homeland's sovereignty and security,” Syria’s state-run news agency SANA quoted a Syrian official source as saying.

Rival Palestinian groups Fatah and Hamas opened talks Sunday in Egypt aimed at implementing a reconciliation agreement struck in May, state news agency MENA reported.

The two sides held consultations late Saturday in the presence of Egyptian intelligence officials, the agency said, adding Fatah's delegation is led by Azzam al-Ahmed and Hamas by Moussa Abu Marzouq.