"We will do this with vetted individuals, vetted units, so it has to be done carefully and appropriately," the official said.

Humanitarian crisis

Meanwhile, the bloodshed continued. On Thursday, 98 people were killed across Syria, including 35 in Damascus and its suburbs, said the Local Coordination Committees for Syria, a network of opposition activists.

The conflict began with demands for political reform after the Arab Spring movement that swept the Middle East and Africa, but devolved into civil war when the al-Assad regime cracked down on demonstrators.

In addition to the 60,000 people who have died since the fighting began in March 2011, another 940,000 have fled the country and more than 10% of Syria's 20 million residents have been forced to move elsewhere inside the country, the Office of the United Nations High Commissioner for Refugees said.

The outpouring of refugees threatens to overwhelm the ability of host nations to provide for their needs, Assistant High Commissioner Erika Feller told the U.N. Human Rights Council on Tuesday.