Sen. John McCain, one of the leading critics of the Obama administration's handling of last month's terrorist attack on the U.S. Consulate in Benghazi, Libya, accused the Pentagon on Friday of not having enough military reinforcements in place to respond to such an attack.

"After three weeks of investigation we have concluded that there was no way that the military could have intervened because they were not ready," McCain, the Arizona Republican, told Fox News. "They were not prepared and there was no alert of any kind that would have enabled them to reach a state of readiness that they could not have intervened."

McCain's comments come as sources tell Fox News that CIA operatives twice asked for permission to help Ambassador Chris Stevens and his staff and were told to 'stand down' — while a later request for military backup was denied. Stevens and three other Americans died in the attack on Sept. 11.

A senior defense official at the Pentagon immediately pushed back against McCain's criticisms, saying his claims "would just be wrong."

The Pentagon says assets were ready but "there were never any requests to deploy assets from outside the country," another senior defense official told Fox News.

The officials, echoing Defense Secretary Leon Panetta's comments Thursday, said that even if military reinforcements could have gotten there in time, there was not a clear enough intelligence picture to do that.

But McCain's office defended the senator's statements.

"Based on documents provided to Senator McCain's staff by the Joint Chiefs that provide a detailed lay down and readiness status of U.S. forces ... as well as follow-up conversations with senior DOD and military officials, it is clear that there were no forces in the region on a high-enough alert status that could have arrived in Benghazi before the fight ended," a statement from the office said.

McCain has asked that these documents, and video taken from a drone flying over the diplomatic compound, be declassified. There have been no responses to that request yet.

"I find it astounding," McCain told Fox News. "I find it a lack of leadership, a lack of understanding, either before or during this attack."