An Iranian American used-car salesman from Texas at the center of a bizarre plot to assassinate the Saudi ambassador to the United States was sentenced Thursday in federal court in Manhattan to 25 years in prison.

Mannsor Arbabsiar, 58, had pleaded guilty in October to a charge of murder-for-hire and two counts of conspiracy for his role in attempting to orchestrate the 2011 bombing assassination of Adel al-Jubeir while the ambassador dined at Cafe Milano, an upscale Georgetown restaurant.

Prosecutors said Arbabsiar was recruited by a cousin who was a senior official in the Quds Force, which in 2007 the Treasury Department designated a terrorist supporter, according to court papers. The group is part of the Revolutionary Guard Corps, which is closely aligned with Iran’s supreme leader, Ayatollah Ali Khamenei.

On Thursday, the State Department said there was a “marked resurgence of Iran’s state sponsorship of terrorism” in 2012, through the Quds Force and other outlets. In its annual report on worldwide terrorism, the department said Quds “is suspected of directing planned terrorist attacks in Georgia, India, Thailand and Kenya in 2012,” along with the 2011 plot.

Preet Bharara, the U.S. attorney for the Southern District of New York, linked Arbabsiar to Iran. “Arbabsiar was an enemy among us — the key conduit for, and facilitator of, a nefarious international plot concocted by members of the Iranian military,” he said. “Our commitment to using every resource we have to root out, prosecute and punish people like Arbabsiar, who act as emissaries for our enemies, remains unflagging.”

Arbabsiar, a serial failure in business, seemed an unlikely conspirator, and Iran denied any involvement in the plot. But prosecutors said he made calls to a Quds Force official after his arrest that the FBI secretly recorded. And despite persistent financial trouble, he made a $100,000 down payment on the $1.5 million fee demanded by a man he thought was a Mexican drug cartel associate who would carry out the bombing. In fact, the purported assassin was a confidential source for the Drug Enforcement Administration.

During a trip to Iran in the early spring of 2011, Arbabsiar’s cousin, Abdul Reza Shahlai, told him that he wanted him to hire someone who could kidnap the Saudi ambassador. Arbabsiar, who lived in Round Rock, Tex., apparently told his cousin and others that he knew people involved in the narcotics business.

Arbabsiar made a number of trips to Iran in 2011, and the plot evolved into a planned assassination. Prosecutors, in arguing for the maximum 25-year sentence, said Arbabsiar understood that any bombing would result in mass casualties but didn’t care.

“No big deal,” he said when given an estimate of 100 to 150 potential casualties at the restaurant, according to the government.

Arbabsiar was arrested in September 2011 after he was refused entry to Mexico and placed on a flight that routed him through New York.

Gholam Shakuri, Arbabsiar’s principal contact in Iran, also was indicted and remains at large.

Defense lawyers had asked U.S. District Judge John F. Keenan to impose a 10-year sentence. They said their client suffered from bipolar disorder and experienced hypermanic episodes. They said his cooperation after his arrest demonstrated “sincere remorse.” Prosecutors said he stopped cooperating.

“Deterrence is of supreme importance,” Keenan said. “Others who might have financial or political purpose in engaging in acts of violence against the United States or its interests must learn the lesson that such conduct will not be tolerated.”