Man charged in plot to attack U.S. shopping mall

* Man had been previously arrested

* Mehanna accused of seeking weapons for mall attack

* Mehanna makes brief court appearance

(Adds court appearance)

By Ross Kerber

BOSTON, Oct 21 (Reuters) - U.S. federal prosecutors have charged a Massachusetts man with conspiracy to provide material support to terrorists, alleging he and co-conspirators traveled to the Middle East seeking training, discussed attacking a shopping center, and distributed videos promoting holy war.

Tarek Mehanna, 27, from Sudbury, Massachusetts, was arrested at his home on Wednesday morning, officials said.

"Mehanna and the co-conspirators had multiple conversations about obtaining automatic weapons and randomly shooting people in a shopping mall, and that the conversations went so far as to discuss the logistics of a mall attack, including coordination, weapons needed and the possibility of attacking emergency responders," the U.S. Justice Department said.

Mehanna had been previously indicted in January 2009 for making false statements to the Federal Bureau of Investigation and other officials in connection with a terrorism investigation, the Justice Department said in a news release.

Prosecutors allege that from 2001 to 2008 Mehanna conspired with a man named Ahmad Abousamra and others in an attempt to kill, kidnap or injure people in the United States.

The charges accuse Mehanna and co-conspirators of talking about their desire to participate in Islamist holy war and to die on the battlefield. The case was based partly on information from two unnamed people described as cooperating witnesses.

Both Mehanna and Abousamra are believed to be U.S. citizens and Abousamra fled the country for Syria in 2006 after federal officials attempted to question him, acting U.S. Attorney Michael Loucks told a news conference in Boston.

Mehanna was arrested about a year ago before boarding a plane at Logan International Airport in Boston and was later released on bail.

Loucks said Mehanna's arrest on Wednesday was unrelated to President Barack Obama's planned visit to Boston this weekend.

The case comes less than a month after an Afghan-born man, Najibullah Zazi, was accused of plotting a bomb attack against the United States.

Authorities say Zazi took a bomb-making course at an al Qaeda training camp in Pakistan, had bomb-making notes on his laptop computer and acquired bomb-making materials similar to those used in the 2005 London attacks.

Attorney General Eric Holder has called that plot one of the most serious security threats to the United States since the Sept. 11, 2001, attacks. Zazi, an Afghan immigrant and permanent U.S. resident, was indicted last month on a charge of conspiracy to use weapons of mass destruction. He pleaded not guilty and was ordered held in prison without bail.

At a preliminary hearing on his case in U.S. District Court on Wednesday, Mehanna did not enter a plea. Speaking to reporters afterward his lawyer, J.W. Carney, did not say how his client would plead.

Mehanna, who has pleaded not guilty to the previous charges against him, was led into a courtroom in handcuffs, wearing a full beard and a black sweatshirt. When Judge Leo Sorokin suggested Mehanna stand up, he snapped back that "I prefer not to." After his father urged him to stand, Mehanna rose to his feet briskly and knocked his chair over, then stood with his hands in his pockets for the rest of the short hearing.

An FBI affidavit on the case says Mehanna and Abousamra came to know Daniel Maldonado, a New Hampshire man now serving a 10-year sentence for getting al Qaeda military training.

According to the government, an unnamed cooperating witness approached Maldonado seeking automatic weapons for a possible attack that Mehanna and Abousamra were planning against an unnamed shopping mall in which they would "randomly shoot people."

But Maldonado said he would be able to obtain only handguns and Mehanna and Abousamra abandoned the plan, a court filing states.

At another point, in 2003, Mehanna, Abousamra and the unnamed cooperating witness discussed whether they could shoot or kill members of the U.S. executive branch, a court filing states. Loucks said U.S. officials were never directly endangered by this.