NEW YORK (CNN) - Manssor Arbabsiar, one of two men implicated in an alleged Iranian plot to assassinate Saudi Arabia's ambassador to the United States, pleaded not guilty Monday in federal court in New York.

The second man indicted in the alleged plot, Gholam Shakuri, remains at large.

Judge John Keenan scheduled the next court date in the case for December 21 to allow the defense time to study documents involved in the discovery process, some of which are classified.

U.S. officials arrested Arbabsiar, 56, on suspicion that he conspired with Shakuri, allegedly an Iran-based member of the Islamic Revolutionary Guard Corps, to hire hit men from a Mexican drug cartel to set off a bomb at a restaurant to be visited by Adel Al-Jubeir, the Saudi ambassador.

The Iranian Foreign Ministry has said the assassination-for-hire accusations are baseless.

Iranian press reports have said Shakuri is an agent of an exiled Mojahedin Khalq Organization (MKO).

In an interview Saturday with CNN's Fareed Zakaria, President Mahmoud Ahmadinejad dismissed the allegations.

"Do we need really to kill the ambassador of a brotherly country? What is the reason and the interest behind that?" he said. "We never have any intention to hurt Saudi Arabia. Do we really want to do it in the United States? And is that the way, really?"