(CNN) -- Al Qaeda leader Ayman al-Zawahiri has allegedly recorded a message telling militants fighting in Syria to unite.
The message, which runs more than five minutes long, was posted on militant websites. Its authenticity could not be independently verified by CNN.
In the message, al-Zawahiri calls upon all jihadi factions to stop infighting.
"Our hearts are bleeding, the heart of our Islamic nation is bleeding when we see the internal strife among the mujahedeen in Syria," he said.
"You are the hope of our Islamic nation in establishing an Islamic governance in the lands of Syria, the chosen land of jihad."
The words may provide verbal ammunition for Syrian President Bashar al-Assad, who has long argued that his forces are fighting "terrorists" in the country's civil war.
But rebels say that al-Assad allowed al Qaeda to grow in Syria in order to defame the revolution.
U.S. says it knew of photos in November
In a separate development, U.S. State Department officials told CNN on Thursday that it was November when the Obama administration found out about photos that allegedly show the Syrian regime committing mass torture.
An activist showed the images to a State Department official on his laptop, officials said.
But the administration did not act on the information because it did not possess the actual files, they said.
The officials said they could not confirm the authenticity of the images, but they think they are genuine.
CNN released a report about the existence of the photos Monday.
The report, by a team of international legal and forensic experts, was based on thousands of photographs provided by a Syrian defector.
The defector claimed to have worked as a photographer at a military hospital that received dead bodies from detention centers.
Syria's Justice Ministry has categorically denied the allegations, branding the report, as "politicized and lacking in objectivity and professionalism."
The Syrian crisis began in March 2011, when peaceful protesters calling for reforms were met by a violent government crackdown. Dissidents began calling for the ouster of al-Assad, whose family has ruled Syria for 42 years.
The conflict spiraled into a civil war that has also ratcheted up sectarian strife between Sunni and Shiite Muslims across the region.
Over the past few years, foreign militants have joined both sides of the war -- including fighters from the Islamic State in Iraq and Syria and Hezbollah fighters from Lebanon.
CNN's Elise Labott contributed to this report.