The divisive Syrian civil war appears to be pitting Hezbollah against Al Qaeda.

Ayman al-Zawahiri, the preacher who replaced Osama bin Laden as Al Qaeda's chief after the latter's death, has urged Islamist militants to put aside their sectarian differences and unite against Syrian President Bashar al-Assad. He made the announcement in a 22-minute recording posted on Islamist militant websites, Reuters reported.

Zawahiri's comments are a reminder of the long-standing fears Syrian opposition activists have had of Al Qaeda co-opting their revolution against Assad.

"Al Qaeda is hijacking the revolution and diverting it from its original purpose, which was toppling the regime," an activist told USA Today late last year.

Based on his latest comments, Zawahiri appears to want Al Qaeda to get involved with the opposition so that militants can have more control over who succeeds Assad.

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"America, its agents and allies want you to shed your blood and the blood of your children and women to bring down the criminal Baathist regime, and then set up a government loyal to them and to safeguard Israel's security," he said.

The recording made the news one day after Lebanese Hezbollah fighters joined forces with Syrian government troops to capture the border town of Qusayr from Syrian rebels.

Iran has also sided with Assad, leading Zawahiri to announce that the Syrian conflict “revealed the ugly face of Iran."

The United States also strongly condemned Hezbollah and the Syrian regime for the Qusayr assault and urged “all parties to avoid actions that could exacerbate the already devastating toll” for civilians.