The United States does not want to see a chaotic demise of the Syrian regime as it could open doors to Islamist extremists to seize power, said CIA Director John Brennan on Friday, Al Arabiya reported.
With the rise of the Islamic State of Iraq and Syria (ISIS) and other militants groups, Washington had reason to worry about who might replace President Bashar al-Assad if his government fell, said the spy chief.
Asked whether the U.S. feared who might succeed Assad, Brennan said: "I think that's a legitimate concern."
Speaking at an event at the Council on Foreign Relations, he said that "extremist elements" including the ISIS group and al-Qaeda veterans are "ascendant right now" in some parts of Syria.
"The last thing we want to do is allow them to march into Damascus."
"That's why it's important to bolster those forces within the Syrian opposition that are not extremists," he added.
Also on Friday, the United Stated made a fresh call for Assad to step down marking the fourth anniversary of the civil war.
Without the departure of Assad, it would not be possible "to fully stabilize" the country, State Department spokeswoman Jen Psaki said.
The U.S. military is funding the training and arming of "moderate" Syrian rebel forces but the effort is only now getting off the ground.
Washington's stance is that Assad should have no role in Syria's future but President Barack Obama's administration and other governments wanted to see a political solution that would ensure a representative government, he said.
"None of us, Russia, the United States, coalition, and regional states, wants to see a collapse of the government and political institutions in Damascus," Brennan said.
The international community favored an eventual settlement that would bring a "representative government that is going to try to address the grievances that exist throughout the country."
Brennan, who worked for years at the spy agency before he became a top counter-terrorism adviser to Obama, took over as the head of the Central Intelligence Agency in March 2013.