Nueces County Sheriff

Mansour Arbabsiar is seen in a 2001 booking photo after he was charged for check fraud.

Updated at 2:30 p.m. ET: A Texas man pleaded guilty Wednesday to plotting to assassinate Saudi Arabia's ambassador to the United States, acknowledging he agreed to hire what he thought was a drug dealer in Mexico last year for $1.5 million to carry out the attack with explosives at a Washington, D.C., restaurant.

Manssor Arbabsiar, 58, entered the plea to two conspiracy charges and a murder-for-hire count in U.S. District Court in Manhattan. Judge John F. Keenan repeatedly asked Arbabsiar whether he intended to kill the ambassador. Arbabsiar, a U.S. citizen who holds an Iranian passport, said he did.

"I take responsibility for my actions," Arbabsiar said.

Arbabsiar also admitted he agreed to help transfer more than $100,000 through a New York bank to help further the plot. 

When Arbabsiar's arrest was announced last year, President Barack Obama's administration accused the Iranian government of being behind the planned assassination of Ambassador Adel al Jubeir in Washington.

The press attache at Iran's mission to the United Nations then called the accusation "baseless."

"Mr. Arbabsiar’s plea today confirms what our investigation had already uncovered: that he plotted to murder the Saudi Ambassador with members of Iran’s elite Qods Force," said FBI Acting Assistant Director Mary Galligan. "The FBI remains ever vigilant toward acts of terror both here and abroad."

Authorities say Arbabsiar earlier admitted his role in a $1.5 million plot to kill the ambassador at a restaurant by setting off explosives. 

See the original story at NBCNewYork.com | More from NBCNewYork.com

Sentencing is scheduled Jan. 23. Arbabsiar faces up to 25 years in prison. A trial had been scheduled for January.

Arbabsiar, who lived in Corpus Christi, Texas, for more than a decade, said he went to Mexico last year to meet a man named Junior, "who turned out to be an FBI agent." He said that he and others had agreed to arrange the kidnapping of ambassador Al-Jubeir, but Junior said it would be easier to kill the ambassador.

Arbabsiar has been held without bail since he was arrested Sept. 29, 2011 at John F. Kennedy International Airport. He was brought into court Wednesday in handcuffs. He spoke English and did not use a translator, despite saying he understood only about half of what he read in English. Bearded and bespectacled, he smiled several times during the proceeding, including in the direction of courtroom artists who were seated in the jury box when he entered court.

Defense lawyers say Arbabsiar suffers from bipolar disorder.

Assistant U.S. Attorney Edward Kim said that if the government had proceeded to trial, it would have presented a jury with secretly recorded conversations between Arbabsiar and a confidential source, along with Arbabsiar's extensive post-arrest statement to authorities and emails and financial records.

Authorities have said they secretly recorded conversations between Arbabsiar and an informant with the Drug Enforcement Administration after Arbabsiar approached the informant in Mexico and asked his knowledge of explosives for a plot to blow up the Saudi embassy in Washington. They said Arbabsiar later offered $1.5 million for the death of the ambassador.

A second person, Gholam Shakuri, was charged in the plot but remains at large in Iran.

The Justice Department said Shakuri is an Iran-based member of Iran’s Qods Force, which is a special operations unit of the Iranian Islamic Revolutionary Guard Corps that is said to sponsor and promote terrorist activities abroad.

Manhattan U.S. Attorney Preet Bharara stated: “As was originally charged, and as Arbabsiar has now admitted, he was the extended murderous hand of his co-conspirators, officials of the Iranian military based in Iran, who plotted to kill the Saudi Ambassador in the United States and were willing to kill as many bystanders as necessary to do so. Arbabsiar traveled to and from the United States, Mexico and Iran and was in telephone contact with his Iranian confederates while he brokered an audacious plot. The audacity of the plot should not cause doubt, but rather vigilance regarding others like Arbabsiar, who are enlisted as the violent emissaries of plotting foreign officials. This office will continue to pursue the co-conspirators in this plot and others in Iran or elsewhere who try to export murder. Thanks to the great work of the FBI, DEA and the prosecutors in this office, Mr. Arbabsiar must now answer for his conduct.”

Pete Williams is NBC News' justice correspondent. Jonathan Dienst is WNBC's chief investigative correspondent. Shimon Prokupecz is a WNBC investigative producer.    

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Husain Haqqani, shown at a memorial service for Pakistan's Minister for Minorities Shahbaz Bhatti in Washington on March 9.

Husain Haqqani, Pakistan's ambassador to the U.S., has resigned amid controversy surrounding a memo he allegedly drafted shortly after U.S. forces killed Osama bin Laden in May.

The memo requested U.S. intervention to prevent a military coup and protect the civilian government in exchange for granting the U.S. heavy influence on matters of national security in Pakistan. 

Dubbed “Memogate,” the affair has dominated headlines in Pakistan for weeks before apparently claiming its first victim on Tuesday.

A statement issued by Pakistan's Prime Minister Yousaf Raza Gilani's office said Haqqani has been asked "to submit his resignation so that the investigation can be carried out properly." 

Haqqani flew back to Islamabad this weekend to explain his involvement – if any -- in the scandal to President Asif Ali Zardari, Prime Minister Gilani and military and intelligence officials, tweeting on Nov.  19th that he was "Heading back to the motherland."  He reportedly offered his resignation then, but it was not accepted at the time. 

"Memogate" is centered on a memo that Pakistani-American businessman Mansoor Ijaz says he delivered to then-chairman of the U.S. Joint Chiefs of Staff, Adm. Mike Mullen, at the behest of Ambassador Haqqani in the days immediately following the U.S. raid that killed bin Laden in Pakistan. The memo, which is unsigned, states that there had been “a significant deterioration in Pakistan’s political atmosphere” and indicated that the civilian government feared that factions within the military were planning a coup.

Read the full memo 

Retired U.S. Gen. Jim Jones, President Barack Obama’s former national security adviser, has confirmed that the memo was delivered to Mullen.

The existence of the memo was revealed in an October op-ed by Ijaz for the Financial Times. Ijaz told NBC News he typed the memo as dictated by Haqqani, and only revealed its existence in the article to lend credibility to the policy case he was making. Haqqani has denied any involvement in requesting or drafting the memo. But opposition leaders in Pakistan pounced, equating the memo to "treason" and demanding that heads roll.

Members of the Pakistani press have been digging into the scandal for the last few weeks, including publishing Blackberry messages allegedly exchanged by Haqqani and Ijaz as the memo was being drafted, and afterward.  

U.S. officials tell NBC News they are watching with "great interest" how this is being handled by the Pakistani government, but say they are not involved in the investigation.

Haqqani, who has been described as a "seasoned political operator," is well-liked within U.S. government circles, and enjoys a strong reputation for managing to remain effective in a treacherous political climate. He remains in Islamabad at this writing.

In Tuesday’s statement, Gilani ordered an investigation to be "carried out fairly, objectively and without bias."

“As a result of controversy generated by  the alleged memo, which had been drafted, formulated and further  admitted to have been received by Authority in USA, it has become  necessary in the national interest to formally arrive at the actual and  true facts,” the statement said. 

Haqqani turned back to his Twitter account following the announcement of his resignation, writing, "I have much to contribute to building a new Pakistan free of bigotry & intolerance. Will focus energies on that."

Fakhar Rehman of NBC News contributed to this report from Islamabad.