By David Schwartz

PHOENIX (Reuters) - An Arizona teenager accused of being an Islamic State sympathizer pleaded not guilty on Tuesday to charges of plotting to attack a Phoenix-area state motor vehicle office with bombs and other weapons and was ordered kept in jail without bond.

Mahin Khan, 18, of Tucson, was arrested by FBI agents on July 1 and indicted last week on state charges of terrorism, conspiracy to commit terrorism and conspiracy to commit misconduct involving weapons.

He faces a maximum penalty of life in prison if convicted with aggravating factors at trial, according to prosecutors.

A not guilty plea was entered by a judge on Khan's behalf to all three counts against him during Tuesday's proceedings. The defendant, who was shackled, said little except to answer perfunctory questions, such as stating his name for the record.

His next court date was set for July 19.

Prosecutors said the charges stemmed from an investigation by the Federal Bureau of Investigation and state authorities of Khan's repeated communications with an individual he believed was an Islamic State fighter.

In the communications, prosecutors said, Khan sought to "obtain weapons including pipe bombs or pressure cooker bombs" for an attack on a Motor Vehicle Division office in Maricopa County.

The identity of Khan's alleged co-conspirator, or whether the person was an informant or undercover FBI agent, has not been disclosed.

In a probable cause statement filed in the case last week, the FBI said Khan described himself in an email as an "American Jihadist who supports" Islamic State, the militant group that has seized large swaths of territory in Syria and Iraq and claimed responsibility for bomb and gun attacks in France, Belgium and Bangladesh.

The document cited an alleged email in which Khan asked a contact he believed to be Pakistani to furnish him with assault rifles and a pistol because he wanted to "take out marines and jews."

It also accuses him of "identifying an Air Force recruitment center in Tucson as a potential target for a terrorist attack," although no such mention is made in the indictment.

The state attorney general's office said last week the investigation of Khan began with citizens alerting authorities to unspecified suspicious behavior.

The judge ordered Khan to remain held without bond. The government has asserted that Khan, who has lived with his family in Tucson since 2011, had indicated he would flee to Syria or Pakistan if released.

(Reporting by David Schwartz; Writing by Steve Gorman; Editing by Peter Cooney)