By Dave Warner

(Reuters) - The embattled mayor of Trenton, New Jersey's state capital, was arrested at his home early on Monday and charged with public corruption, the FBI said.

The charge against Trenton Mayor Tony Mack involves conspiracy to obstruct commerce by extortion, said Barbara Woodruff, FBI spokeswoman in Newark, New Jersey.

The mayor has been the target of an ongoing federal investigation, and in July FBI agents staged an early morning raid on his home and searched offices in City Hall as well.

Mack has been accused by critics of nepotism and mismanagement since taking office in the crime-plagued, economically depressed city of 85,000 in 2010.

He was arrested at his home at about 6:30 a.m. EDT, the FBI said.

Also arrested on Monday was a longtime associate of Mack, Joseph Giorgianni, also for public corruption, the FBI said. Giorgianni also faces drug charges, it said.

In July, after the FBI raid on his home, Mack said he had done nothing wrong.

"We have not violated the public trust in any way," he said at the time.

An effort to recall Mack, a Democrat, failed last year when organizers did not get enough support to force a special election.

Mack was slated to appear before a federal magistrate in Trenton later on Monday, and U.S. Attorney Paul Fishman and Michael Ward, director of the FBI in New Jersey, planned to hold a news conference in Trenton later on Monday as well, the FBI said.

(Editing by Ellen Wulfhorst and Eric Beech)