Tehran (CNN) - Iran's top cleric blamed the CIA and Mossad, Israel's intelligence agency, for the killing of an Iranian nuclear scientist, Iran's state broadcaster said late Thursday.

Mostafa Ahmadi Roshan, who died Wednesday, was the third Iranian nuclear scientist to be killed by a bomb placed underneath his car in the past two years. A fourth survived a similar assassination attempt.

Roshan's death shows that "the global arrogance spearheaded by the U.S. and Zionism has reached a deadlock in confrontation with the determined, devout and progressive nation of Islamic Iran," Supreme Leader Ayatollah Ali Khamenei was quoted as saying by Press TV.

Those responsible will not own up, Khamenei said, but the attack "has been carried out by the planning or support of CIA and Mossad [spy] services, like all other crimes of the network of international state terrorism."

(CNN) - A Syrian opposition group demanding the end of President Bashar al-Assad's reign announced Friday that it has begun coordinating with the rebel Free Syria Army, while thousands of anti-government protesters were set to take to the streets to support the breakaway army.

The announcement by the Syrian National Council and the planned protests across the country in support of the rebel army appears to signal a shift in the anti-government movement, an effort to solidify coordination between the groups who say have been the target of a brutal crackdown by al-Assad's forces.

The move coincides with reports of increased violence against demonstrators by security forces despite the ongoing efforts of an Arab League fact-finding mission to determine whether the Syrian government is abiding by an agreement to end the crackdown.

Al-Assad, who has characterized the anti-government protesters as "armed gangs," has insisted his security forces are battling terrorists intent on targeting civilians and fomenting unrest. The United States, the European Union and a number of Arab countries have called on al-Assad to end the violence and step down.