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.
U.S. officials have said the alleged scheme involved a connection to the Quds Force, a branch of the Islamic Revolutionary Guard.
Iranian press reports have said Shakuri is an agent of an exiled Iranian opposition group.
In an interview Saturday with CNN's Fareed Zakaria, Iranian 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?"
Authorities developed the case against the suspects with the help of an undercover informant posing as an associate of a Mexican drug cartel, according to officials and an FBI agent's affidavit.
Arbabsiar and the informant allegedly discussed using explosives to kill the ambassador, possibly in a crowded restaurant, according to the affidavit.
The informant named $1.5 million as his price, it said. Arbabsiar told the informant his "cousin" has deep pockets, court documents say, and allegedly sent $100,000 intended as a down payment.
According to the five-count indictment, Arbabsiar wired money to an undercover bank account maintained by the FBI. In the spring, Shakuri provided money to Arbabsiar for expenses, it contends.
Arbabsiar was arrested in September.
Both defendants are charged with conspiracy to murder a foreign official; conspiracy to engage in foreign travel and use interstate and foreign commerce facilities in the commission of murder-for-hire; conspiracy to use a weapon of mass destruction (explosives); and conspiracy to commit an act of international terrorism transcending national boundaries.
Arbabsiar also is charged with a count of foreign travel and use of interstate and foreign commerce facilities in the commission of murder-for-hire, prosecutors said.
CNN's Jim Barnett contributed to this report.