Iraq and Syria have been so thoroughly damaged by warfare, sectarian conflict and killing that it is unclear they "can be put back together again," CIA Director John Brennan said.

In an interview this week with the CTC Sentinel, a publication from the West Point military academy's Combating Terrorism Center, the head of the Central Intelligence Agency said the current system of governance in the two countries might change altogether.

"I don't know whether or not Syria and Iraq can be put back together again. There's been so much bloodletting, so much destruction, so many continued, seething tensions and sectarian divisions," Brennan said.

"I question whether we will see, in my lifetime, the creation of a central government in both of those countries that's going to have the ability to govern fairly."

He added that he could envision some type of a federal structure governing autonomous regions.

Meanwhile, more than 70 Syrian aid groups are suspending cooperation with the United Nations, accusing UN humanitarian agencies and their partners of being manipulated by the regime, according to a letter released yesterday.

In the letter to the UN Office for the Coordination of Humanitarian Affairs (OCHA), the 73 signatories

demanded an investigation of the UN agencies' work in Syria and called for a monitoring body to be set up to oversee the relief effort.

“Our goal is to deliver as much aid as possible," said UN spokesman Stephane Dujarric, who rejected suggestions that UN aid workers were influenced by the government in Damascus.

The US yesterday pressed Russia for a "true cessation of hostilities" in Syria ahead of expected high-level peace talks in Geneva, warning that its patience is running thin.

Foreign ministers from the two powers, which support opposite sides in the five-year conflict, were poised to hold a "personal meeting" in the Swiss city to push for a peace agreement, according to the Russian side.

And US Defense Secretary Ash Carter told BBC radio there was "quite a long way to go" before a final deal could bestruck.

The development came after US President Barack Obama held talks with his Russian counterpart Vladimir Putin on the sidelines of the G20 summit in China but failed to bridge their differences.

Pro-regime forces also overran a strategically important district on the southern outskirts of Aleppo Thursday, rolling back nearly every gain from a major month-long rebel offensive there, said the Syrian Observatory for Human Rights.