Rep. C.A. Dutch Ruppersberger of Maryland, the top Democrat on the House Intelligence panel, also supported the department's decision to go public with its concerns.
"The most important thing we have to do is protect American lives," he said, describing the threat as "not the regular chitchat" picked up from would-be militants on the Internet or elsewhere.
The State Department issued another warning a year ago about potential violence connected to the Sept. 11 anniversary. Dozens of American installations were besieged by protests over reports of an anti-Islam video made by an American resident, and in Benghazi, Libya, the U.S. ambassador and three other Americans were killed when militants assaulted a diplomatic post.
The administration no longer says Benghazi was related to the demonstrations. But the attack continues to be a flashpoint of contention with Republicans in Congress who say Obama, former Secretary of State Hillary Rodham Clinton and others in the government misled the country about the nature of the attack after failing to provide adequate diplomatic protection.
Associated Press writers Donna Cassata, Sagar Meghani and Kimberly Dozier in Washington and Jill Lawless in London contributed to this report.