UNITED NATIONS—U.N. Secretary General Ban Ki-moon cast doubt on U.S. and French intelligence on the alleged chemical attack in Damascus and warned against a U.S. military intervention.

"We should avoid further militarization of the conflict and revitalize the search for a diplomatic settlement," Mr. Ban told a news conference at U.N. headquarters in New York on Tuesday. "We must consider the impact of military intervention," which he said could increase bloodshed.

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