Mexico worked closely with U.S. authorities to help foil an alleged $1.5 million plot to kill the Saudi Arabian ambassador to Washington, a foreign ministry official said Tuesday.

Mexico issued an immigration alert on Manssor Arbabsiar, 56, after U.S. authorities told Mexican counterparts that Arbabsiar was the subject of an arrest warrant for "serious crimes," said Julian Ventura, undersecretary for North America.

Ventura told reporters that the alert prompted Mexican immigration officials to turn Arbabsiar away when he tried to enter Mexico on Sept. 28. Arbabsiar, a U.S. citizen who holds an Iranian passport, was arrested the next day when he arrived at New York's Kennedy International Airport.

Ventura did not say where Arbabsiar tried to enter Mexico, but an immigration official said later that it was at the airport in Mexico City. The official agreed to discuss the matter only on condition of anonymity because he was not authorized to speak about the case.

Arbabsiar was charged Tuesday in U.S. District Court in New York with conspiring to kill the Saudi diplomat, Adel Al-Jubeir.

U.S. authorities allege Arbabsiar was attempting to meet in Mexico with a U.S. informant posing as a Mexican drug cartel associate. U.S. authorities allege he hired the informant for $1.5 million to carry out the assassination with a bomb attack while Al-Jubeir dined at his favorite restaurant.

Court documents say Arbabsiar and the informant had met in Mexico before Sept. 28, though authorities have not said where. They said he often traveled to Mexico on business.

"From the outset, Mexico and the United States exchanged information and acted together," Ventura said, reading a statement on the operation. "The government of Mexico reiterates its full commitment to international cooperation to prevent and combat terrorism and condemns any attempt by any individual, group or international player to commit actions of this nature from our national territory."

The undersecretary said the information was shared through protocols the two countries already had established, particularly on matters of regional security and justice. He did not answer any questions.