Christians Under Attack

Officials said no weapons or bomb-making materials had been found in the searches in the Miami area by FBI and state and local law enforcement officials. The city is under no imminent threat, according to the FBI.

Law enforcement sources told CNN that the arrests disrupted what may have been the early stages of a domestic terrorist plot to attack the Sears Tower in Chicago, Illinois, the FBI building in Miami, and possibly other targets. (Watch details of the raids -- 2:53)

The 110-story Sears Tower is the world's third-tallest building and the tallest in North America.

Barbara Carley, managing director of the Sears Tower, said in a statement that "it would be inappropriate for us to confirm or deny details of news reports about federal law enforcement action before an official statement from the Justice Department.

"However, Sears Tower security officials regularly speak with the FBI and local law enforcement authorities who track and investigate terrorism threats. Today was no exception," she said. "Despite new information, law enforcement continues to tell us that they have never found evidence of a credible terrorism threat against Sears Tower that has gone beyond criminal discussions."

Law enforcement sources told CNN that some of the suspects are members of a radical Muslim group and that at least one had taken "an al Qaeda oath." They had carried out surveillance on the Sears Tower and FBI building in Miami, the sources said.

Federal law enforcement sources said five of the seven men were Americans, one was an illegal immigrant from Haiti whose visa had expired and the seventh was a resident alien.

Sources told CNN that the arrests culminated a monthslong undercover operation. The suspects believed they were dealing with an al Qaeda operative but the person was actually a government informant, the sources said.

Documents related to the investigation have been sealed.

One of the arrests was made before Thursday, officials said, and one of Thursday's arrests took place in Atlanta, Georgia.

A spokeswoman for Miami-Dade Mayor Carlos Alvarez said the mayor was notified of the raid earlier in the day, and a spokesman for Florida Gov. Jeb Bush said the governor had been notified Thursday morning.

Both Alvarez and Bush said they had no plans to tighten security.

"If anything, this is a plot foiled," Alvarez spokeswoman Vicki Mallette said.

Plans for a massive rally Friday in the city for the Miami Heat, the new National Basketball Association champions, are unchanged, she said, adding that 200,000 people were expected to attend.

The FBI said one search warrant was executed in a warehouse near a housing project in Liberty City, a predominantly black and low-income area of Miami.

Cedric Thomas, a co-owner of Thomas Produce Market, told the Miami Herald that the area around his store was teeming with federal agents.

''There is a ton of guys in uniforms moving around, blocking the streets. I'm not sure what they are doing,'' Thomas told the newspaper.

Neighbors told CNN the men, who wore turbans, caused no problems but acted oddly.

"All you could do was just see their eyes. They had their whole head wrapped up. Just the eyes showing. And they were standing guard -- one here, one there -- like soldiers. Very quiet," one woman said.

A man said the men never spoke to neighbors and would just nod their heads if spoken to.

"They was acting like they was in military training," he said.

Residents living near the warehouse told The Associated Press that the men taken into custody called themselves Muslims and had tried to recruit young people.

The men slept in the warehouse, Tashawn Rose, 29, told the AP.

"They would come out late at night and exercise," she said. "It seemed like a military boot camp that they were working on there. They would come out and stand guard."

The residents told the AP that FBI agents spent several hours seeking information from people in the neighborhood. They said the suspects, who appeared to be in their teens or 20s, had lived in the area for about a year, the AP reported.

"We are conducting a number of arrests and searches, and we'll have more about that when the operation is completed, probably tomorrow morning," FBI Director Robert Mueller told CNN's Larry King in an interview broadcast Thursday night.

"Because it's an ongoing operation, we really can't get into details," Mueller said. "But whenever we undertake an operation like this, we would not do it without the approval of a judge. We've got search warrants and arrest warrants and the like."

In a statement, the U.S. attorney's office in Miami said federal, state and local agencies made the arrests in connection with a domestic "terrorist-related matter."

Attorney General Alberto Gonzales will hold a news conference Friday regarding the raids.