"As international support for Obama’s decision to attack Syria has collapsed, along with the credibility of government claims, the administration has fallen back on a standard pretext for war crimes when all else fails: the credibility of the threats of the self-designated policeman of the world," Chomsky told Huffington Post newspaper on Monday.

Chomsky recently traveled to the region to learn more about the Syria crisis, and his comments there led some to believe he was open to military intervention if negotiations failed to produce peace.

"I believe you should choose the negotiating track first, and should you fail, then moving to the second option" -- backing the rebels -- "becomes more acceptable," he said.

But his comments to HuffPost indicate that he remains opposed to any military action that came without UN approval.

"That aggression without UN authorization would be a war crime, a very serious one, is quite clear, despite tortured efforts to invoke other crimes as precedents," he added.

Liberals more associated with the establishment than Chomsky, who have nevertheless tended to be critical of the president's foreign policy, cheered his decision to involve Congress as a step away from an increasingly imperial presidency and toward more democratic accountability of war making.

Chomsky upended the field of linguistics with a devastating critique of B.F. Skinner in 1959 that changed the way people think about human cognitive development. He has led a parallel career as a leading anarcho-syndicalist author, historian and activist.

NTJ/BA