NBC:

Iran is pushing back against U.S. efforts to strengthen sanctions against Tehran in response to an alleged plot to assassinate the Saudi ambassador to Washington, demanding a public apology and unspecified monetary damages, an Iranian diplomat tells NBC News.

The Iranian demands were contained in a recent letter to the U.S., according to the diplomat, who spoke on condition of anonymity. It calls on the U.S. to apologize publicly to both the Islamic republic and officials of the Al Quds Force for “material and moral damages” caused by “this baseless accusation,” which it argues violated “international rules and regulations.”

The letter states that such deception has become “a permanent part of statecraft in the U.S.,” according to the source, citing as an example the U.S. invasion of Iraq, which it says was “based on such false information.”

“After killing hundreds of thousands of innocent Iraqis and U.S. soldiers and wasting billions of dollars from the U.S. citizens’ pocket, the U.S. has no other way out except leaving Iraq,” the diplomatic source said, recounting the argument made in the letter.

The diplomatic source would not provide details on when the letter was sent out, to whom it was addressed or who in the Iranian government wrote it.

A State Department representative acknowledged Sunday that a letter had been received, but declined to discuss its contents.

The spokesperson added that the two sides are talking about the alleged plot, saying the U.S. “is still in contact with Iran regarding this case and continue to receive non-constructive responses.”

The letter raises the stakes in a diplomatic standoff arising from the indictment last month of an Iranian American and an Iranian on terrorism and other charges related to the alleged plot.

U.S. officials have cited the plot as the latest example of Iranian terrorism and evidence of its increasing extremism. At the same time, Iranian officials at all levels of the government, including Supreme Leader Ali Khamenei, have excoriated the U.S.

“If U.S. officials have some delusions, (they must) know that any unsuitable act, whether political or security, will meet a resolute response from the Iranian nation,” Khamenei warned two weeks ago on Iranian television, suggesting the allegations may be used by the Obama administration to justify war.

President Mahmud Ahmadinejad said similarly that “Iran is a civilized nation and doesn’t need to resort to assassination.”

“The culture of terror belongs to you,” he said, referring to the United States.

Iran also has demanded that a diplomat be allowed to visit the Iranian American suspect, Manssor Arbabsiar, in prison, a request that has yet to be honored.