The United States has had "direct contact" with Iran over the alleged involvement of the Iranian government in a plot to assassinate the Saudi ambassador to Washington, U.S. State Department spokeswoman Victoria Nuland said on Thursday.

Manssor Arbabsayar, one of the suspects charged with?plotting assassination?of?the Saudi ambassador to the United States [File photo]

"We have had direct contact with Iran on this issue," Nuland said at a regular news briefing.

She declined to offer more details, saying only that she believed the contact took place on Wednesday in a place other than Iran.

"We are not prepared at the moment to go any further on the question of who spoke to whom, and where, but just to confirm that we have had direct contact with Iran," she explained.

On Tuesday, the U.S. Justice Department alleged that two men, Manssor Arbabsayar, a 56-year-old U.S. citizen holding both the Iranian and U.S. passports, and Gholam Shakuri, an Iranian citizen, were charged with sponsoring and promoting terrorist activities abroad, including a plot to kill the Saudi Ambassador to Washington Adel Al-Jubeir.

The U.S. authorities said that three other men, all senior officers like Shakuri from the Quds Force, an elite division of Iran's Revolutionary Guard Corps responsible for foreign operations, were involved in the plot.

U.S. President Barack Obama said on Thursday that there would be "no dispute" over U.S. claim after people have analyzed the facts before them.

He called the plot "not just a dangerous escalation," but "part of a pattern of dangerous and reckless behavior by the Iranian government," vowing to seek the "toughest sanctions" against Iran.