The Arab League has given Syria until Sunday to respond to a proposal that would send observers into the violence-torn country as part of a plan to end a military crackdown on protests there.

Qatar's Foreign Minister Sheikh Hamad bin Jassim al-Thani said league officials reacted to requests by Damascus for some clarifications to the initiative but did not make any key changes.

Senior league officials have said that failure to reach an agreement could lead to outside involvement in the Syrian crisis.

Meanwhile, Reuters said Sunday that at least a dozen secret police have defected from an intelligence compound in Idlib province, near the Turkish border. Clashes between Syrian government forces and dissident soldiers in the restive northern province killed at least 15 people on Saturday.

Activists say at least 25 people died across Syria in anti-government unrest Saturday. Witnesses say battles have been intensifying in recent days as more soldiers defect from regular army units.

The Arab League on Saturday froze assets of 19 top Syrian officials and banned them from traveling to Arab states.

Syria's failure to meet an earlier league deadline resulted in the enactment of a series of measures including a ban on dealings with the central bank, a halt to Arab funding of projects in Syria and a freezing of Syrian government assets.

In Istanbul Saturday, visiting U.S. Vice President Joe Biden praised Turkey for taking steps to address repression in Syria. He added his voice to those calling for Syrian President Bashar al-Assad to step down.

The United Nations says the overall death toll from eight months of unrest in Syria has topped 4,000. A U.N.-backed study says several hundred children are among those killed in the government crackdown.

Syria has contended its actions are not a crackdown on protests, but a necessary response to attacks by “armed terrorists” on civilians and security personnel.