"The president believes that on principle it's important to release that report, so that people around the world and people here at home understand exactly what transpired," he added.

The State Department has put its missions around the world on watch, and asked them to review security arrangements ahead of the report's release "given the range of possible reactions overseas."

"We're in close touch with them, but I'm not going to get into any specifics about security at our embassies," State Department spokeswoman Jen Psaki said.

She confirmed Kerry had spoken with Feinstein last week about the "foreign policy implications of the release of the report". He had raised "everything from our ongoing efforts related to ISIs, the safety of Americans being held hostage around the world," Psaki said, referring to the growing coalition to fight ISIS (Islamic State in Iraq and Syria) militants.

"He was simply having a discussion about the impacts that the release will have on those factors," she said, adding that timing of the report remained up to Feinstein.

But another State Department official, who asked not to be named, said "you could infer that he talked about delaying the release." US embassies have frequently been the target of violent protests, particularly in Arab and North African countries.

In September 2012, on the anniversary of the 2001 attacks, US ambassador to Libya Chris Stevens, and three other Americans, were killed when heavily-armed militants stormed a US mission in Benghazi, eastern Libya.