NEW YORK (CNN) -- Federal agents raided residences in New York City early Monday as part of a terrorism investigation, law enforcement sources said.

Sen. Charles Schumer, D-New York, said the raids were "preventive" but not related to the president's visit.

Sen. Charles Schumer, D-New York, confirmed the raids in an interview with CNN affiliate WABC.

"There was nothing imminent, and our law enforcement officials are very good now at tracking potentially dangerous actions," Schumer said, speaking from Washington. "This was preventive."

Schumer said the raids were unrelated to President Obama's visit to New York on Monday for a speech. Citing "speculation the two were related," Schumer said: "They're not." Watch witnesses react to raid »

But two other sources contradicted Schumer, telling CNN that authorities had acted in part because of concerns that the president would be in town. There was no indication of a specific plot against the president, the sources said. One of those sources, a member of Congress, said authorities took action "out of an abundance of caution."

Another member of Congress, Republican Rep. Peter King of New York, confirmed the raids to CNN.

"I can tell you that the raids were carried out -- in Flushing [and] Queens. There was a search warrant and there is an ongoing investigation, and it's being treated very seriously," King said. "As far as I know, there are no arrests."

A source at the New York Police Department confirmed to CNN that the Joint Terrorism Task Force executed multiple search warrants early Monday at more than one building in Flushing, Queens, a borough of New York City. The source said the search warrants were part of an ongoing investigation, but provided no further information on the number executed.

A federal law enforcement source confirmed the Joint Terrorism Task Force's involvement in the raids, adding that agents were searching for a particular individual who wasn't at the raided buildings.

In Washington, the chairman of the House Homeland Security Committee, Rep. Bennie Thompson, D-Mississippi, was briefed Monday on the situation, a congressional source told CNN. A spokesman for Thompson declined to comment further, saying the briefing was classified.

Schumer told WABC he was unable to provide further information due to the classified nature of the case. He said the FBI and New York City Police Department told him they would provide further information when appropriate.

The raid happened in the early morning and involved dozens of agents, some wearing FBI jackets, some wearing suits, and many carrying weapons, according to an eyewitness who lives in one of the raided buildings.

The witness said agents emerged from one building carrying a black document box.

CNN's Deirdre Walsh, Deb Feyerick and Kiran Khalid contributed to this report.

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