One of the suspects accused in a plot to assassinate the Saudi ambassador to the United States has pleaded not guilty.

Manssor Arbabsiar, a naturalized U.S. citizen holding Iranian and American passports, entered his plea in a New York court Monday. He is charged with trying to hire a Mexican drug cartel to kill Saudi envoy Adel al-Jubeir by bombing a Washington restaurant.

U.S. officials have alleged that Arbabsiar was part of a $1.5 million plot by the Iranian Revolutionary Guard’s elite Quds force to kill the Saudi ambassador. A second suspect, Gholam Shakuri, is at large, but is believed to be in Iran.

Iran has denied involvement in the case. Iranian President Mahmoud Ahmadinejad told the CNN television network on Sunday that “we never have any intention to hurt Saudi Arabia.”

The 56-year-old Arbabsiar has lived for many years in the U.S., working as a used car salesman in Texas.