A prominent Druze cleric known for criticizing Syria's regime and Islamist extremists was assassinated in a car bomb attack outside the southern city of Sweida Friday, a monitoring group said.

"Sheikh Wahid al-Balous was killed in a car bomb attack as he was driving on the outskirts of Sweida city," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

Britain will take in thousands more Syrian refugees, Prime Minister David Cameron said Friday amid growing pressure at home and abroad to address the crisis.

"Given the scale of the crisis and the suffering of the people, today I can announce that we will do more, providing resettlement for thousands more Syrian refugees," he told reporters on a visit to Lisbon.

Islamic State group jihadists have blown up several of ancient Palmyra's famed tower tombs as they press their demolition of the UNESCO-listed world heritage site, Syria's antiquities chief said Friday.

IS has carried out a sustained campaign of destruction against heritage sites in areas under its control in Syria and Iraq, and in mid-August beheaded the 82-year-old former antiquities chief in Palmyra.

The father of a drowned Syrian toddler whose fate shocked the world returned home Friday to bury his family as European ministers tried to thrash out differences on binding refugee quotas to ease the crisis.

Britain said it would take thousands more from refugee camps on the Syrian border as the heartbreaking images of three-year-old Aylan Kurdi's lifeless body on a Turkish beach ramped up pressure on political leaders to act.

The White House on Thursday said it was closely monitoring reports that Russia is carrying out military operations in Syria, warning such actions, if confirmed, would be "destabilizing and counter-productive." 

"We are aware of reports that Russia may have deployed military personnel and aircraft to Syria, and we are monitoring those reports quite closely," said spokesman Josh Earnest. 

Iran submitted last month a peace plan to Syrian President Bashar Assad to try and end his country's four-year war, a senior Iranian official said on Thursday.

Iranian Deputy Foreign Minister Hossein Amir-Abdollahian however told a news conference in Damascus that any initiative to end the conflict would have to recognize "the pivotal role of Assad."

Egyptian billionaire Naguib Sawiris has offered to buy an island off Greece or Italy and develop it to help hundreds of thousands of people fleeing from Syria and other conflicts.

The telecoms tycoon first announced the initiative on Twitter.

U.N. investigators on Thursday denounced the international community's failure to protect refugees fleeing Syria, saying the neglect of those forced to flee the conflict had fueled Europe's migrant crisis.

In its latest report, the United Nations Commission of Inquiry on Syria said the responsibility to protect Syrian refugees "is not being adequately shared or shouldered."

Polish Prime Minister Ewa Kopacz said Thursday she was against any quota plan to share migrants across the 28-member European Union but was open to raising the numbers Warsaw took in.

The EU has been overwhelmed by the massive crisis as hundreds of thousands of people try to reach the bloc by sea and land after fleeing conflicts in Africa, Asia and the Middle East.

The family of toddler Aylan whose lifeless body washed ashore on a Turkish beach had been repeatedly displaced by Syria's brutal four-year war, a local journalist said Thursday.

Images of the child wearing a red T-shirt and blue shorts spread like wildfire through social media and his plight has dominated international headlines, in a heart-rending symbol of the mortal risks faced by tens of thousands of refugees desperate to reach Europe by sea.