The rebel Free Syrian Army (FSA) has offered a $25 million reward for the capture, dead or alive, of Syrian President Bashar al-Assad, Turkey's Anadolu news agency reported on Tuesday.

FSA commander Ahmed Hijazi said the money will be paid out by supporters as well as by "Syrian businessmen working both at home and abroad."

The United States said last month it had set aside $25 million for non-lethal aid to Syrian rebels.

The bounty offer comes as Western powers are looking to put more pressure on President Assad to go.

Lakhdar Brahimi, the UN and Arab League envoy to Syria, has warned that crisis presented a "threat to the Syrian people, the region and the world."

Activists say some 23,000 people have died since the uprising against President Assad began in March last year.

The Damascus government insists it is combating "armed terrorist gangs" who are seeking to destabilize Syria.