The former Syrian prime minister has called the Assad government an "enemy of God."
Speaking at his first public appearance since his defection to the opposition earlier this month, Riyad Hijab told a news conference in Jordan that the morale of Syrian authorities was low after grappling for 17 months to crush a popular uprising against Assad.
Syrian authorities said they had dismissed Hijab before he fled, but he told the news conference that he defected to the opposition.
"The regime is collapsing, spiritually and financially, as it escalates militarily.
"It no longer controls more than 30 percent of Syrian territory."
"It is my duty to wash my hands of this corrupt regime," he said.
Middle East Correspondent John Ray reports:
Hijab, who recently had sanctions placed on him by the U.S lifted, did not explain his estimate of the territory still controlled by Assad, whose military outnumbers and outguns the rebels fighting to overthrow him.
The army is struggling to regain control of Aleppo, Syria's biggest city, after retaking parts of Damascus that were seized by insurgents last month.
UN Humanitarian chief Baroness Amos arrived in Syria today to discuss civilian aid, with the UN estimating that 2.5 million are now in need of assistance.