Intercepted call reportedly clinched US claim on Syria chemical weapons strike

U.S. intelligence officials were able to confirm that chemical weapons were used in Syria last week in part because they intercepted panicked phone calls in which a Syrian defense official demanded an explanation for the attack from an official in a chemical weapons unit, according to a new report.

Foreign Policy reported Wednesday that U.S. intelligence overheard the phone calls, which helped drive the Obama administration to the unequivocal declaration this week that chemical weapons were deployed.

The phone calls, as well as photo evidence and local accounts, are part of the portfolio of evidence the U.S. is preparing before proceeding with a response -- likely a military strike, according to sources -- in the coming days.

The intercept, though, raises questions about the nature of last week's attack. If a Syrian defense official was questioning the chemical weapons unit about the attack, it raises the possibility that it was a rogue event -- or, to the contrary, cleared at the highest levels, without the say-so from mid-level defense officials.

"It's unclear where control lies," one unnamed intelligence official reportedly told Foreign Policy.

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    One official added that the U.S. does not know why the attack happened. "We just know it was pretty f------ stupid."

    Obama administration officials have said it is now "undeniable" that chemical weapons were used, and claim to be practically certain that the Assad regime was behind the attack. They plan to present their evidence publicly in the coming hours and days, while claiming to await support from top allies before proceeding with any response.

    A British Parliament vote is not expected until Thursday. While members of Congress in Washington are demanding some role in any Syria decision, it's not clear to what extent the administration will seek their counsel or consent.

    It's also unclear whether the U.S. will wait for approval from the United Nations.

    The U.N.'s special envoy to Syria, Lakhdar Brahimi, said Wednesday, after a preliminary investigation, that evidence suggests that some kind of chemical "substance" was used in an attack that killed hundreds of people.

    But Brahimi said any military strike on Syria must have U.N. Security Council approval. Brahimi said "international law says that any U.S.-led military action must be taken after" agreement in the 15-nation Security Council.

    He added that President Obama's administration is "not known to be trigger-happy."

    British Prime Minister David Cameron now says he plans to seek input from the U.N. Security Council.

    He tweeted that Britain has drafted a resolution condemning the attack and authorizing "necessary measures to protect civilians." He said the resolution will be presented before the five permanent members of the Security Council in New York on Wednesday.

    The Associated Press contributed to this report.