Updated

Anti-terror raids conducted in New York City early Monday morning were part of an investigation into an Al Qaeda associate, law enforcement agents told FOXNews.com.

The Afghani resident, who has been living in the Midwest, has been under federal surveillance and is believed to have visited over the weekend more than one of the Flushing, Queens residences searched by Joint Terrorism Task Force agents, the sources said.

New York Police Department spokesman Paul Browne confirmed that searches were conducted in Queens by task force agents but would not discuss the matter further.

Two U.S. intelligence officials, who requested anonymity because they were not authorized to discuss the case publicly, said the target of any purported attack -- or who would carry it out -- remained unclear.

Authorities have not found any weapons ready for use -- such as a bomb -- that would indicate an attack was imminent, they said. Nevertheless, one of the officials called the threat very real and emphasized the urgency of the threat.

Another person briefed on the matter, who was not authorized to discuss the case and requested anonymity, said the raids were the result of previous law enforcement surveillance of individuals and the investigation was continuing.

Sen. Charles Schumer, D-N.Y., who was briefed by FBI officials, said he couldn't discuss much of the case because many of the details were still classified.

"There was nothing imminent, and they are very good now at tracking potentially dangerous actions and this was preventive," Schumer said. He added that the law enforcement action was unrelated to President Barack Obama's visit Monday to New York.

Monday afternoon, a man answering his apartment door at a three-story brick apartment building in a predominantly Asian neighborhood of Queens confirmed that police had been at his apartment earlier Monday. He and a woman in the apartment wouldn't comment further or identify themselves, closing their door to a reporter.

Nearby resident Kabir Islam, 24, said he saw FBI agents and police officers surrounding the apartment when he arrived home after 3 a.m. Monday.

The Associated Press contributed to this report.