Officials bolster security, but not threat warning

"This is sobering information about those who wish to do us harm," Ridge said at a news conference.

Federal officials have no specific information about where and when an attack could take place, Ridge said. The nation's threat level will remain at yellow, or "elevated," for now, but federal officials are implementing heightened security measures, he said.

FBI Director Robert Mueller and Homeland Security Undersecretary Asa Hutchinson briefed House members Wednesday about efforts to bolster security for this summer's political conventions, but Hutchinson said there is no need to raise the nation's threat level.

"There is a consistent stream of intelligence reporting that shows [terrorist groups] want to attack the United States," said a Homeland Security spokesman. "We remain concerned about the threat during this increased period of risk."

The spokesman said the briefing was scheduled to update Congress on current threats and the department's efforts to strengthen security before the political conventions in Boston at the end of July and New York City in late August and early September.

House Homeland Security Committee Chairman Christopher Cox, R-Calif., who also attended the briefing, said a "steady drumbeat" of intelligence data shows the "terrorist threat has not abated."