Al Qaeda chief tells Syrian rebels: Unite or die

The elusive leader of Al Qaeda released over the weekend his first audio message to followers in several months, calling on jihadists fighting in Syria's civil war to come together.

CBS News' Khaled Wassef reports Ayman al-Zawahiri said rebels should join with the Al Nusra Front, Al Qaeda's representative in the five-year-old conflict and one of the two most powerful groups fighting Syrian government forces outside of the Islamic State of Iraq and Syria (ISIS.)

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Al Nusra and ISIS were once joined, but split in 2013 amidst a power struggle.

Zawahiri said there are numerous forces jihadists must fight in Syria, from Russia to the Assad regime to Shiites.

"We have to want the unity of the Mujahideen in Sham (Syria) so it will be liberated from the Russians and Western crusaders. My brothers ... the matter of unity is a matter of life or death for you," Zawahri said, according to Reuters.

Zawahiri clearly stressed that this call to unity in not directed towards ISIS, Wassef reports.

The al Qaeda chief has released similar messages in the past. In 2014 he released a plea for rival Islamic groups in Syria to end their infighting and focus on battling President Bashar Assad's forces.

Al-Zawahri said at the time the internal fighting "between the holy warriors of Islam has bloodied our hearts" and that it should stop immediately. He called on Islamic groups in Syria to set up an Islamic court that would mediate and resolve their differences.

He said Islamic fighters should focus on "bringing down Assad's secular, sectarian, unjust and criminal regime to set up a just Islamic state."

The plea did not succeed.