Iran on Tuesday denounced US President Barack Obama for keeping the "threat" of military force on the table to coerce the Islamic state into curbing its controversial nuclear activities.
"It is a source of regret that he still uses the language of threat after we told them to replace it with one of respect," Iranian foreign ministry spokeswoman Marzieh Afkham told reporters.
In an earlier statement, Afkham said it was "unjustifiable" that the White House could "violate international rules and the UN charter to cater to the interests of lobbies by resorting to the military option."
In the statement, carried in local media, she also denounced Obama's comments that Iran should not see his holding off of action against Syria as a sign Washington would not strike Iran.
"The Obama government must understand that the use of the language of threats against the Islamic republic of Iran will not have the slightest effect on the determination of the government and the nation to defend their absolute nuclear rights, particularly on enriching uranium," she said.
In an interview with ABC News on Sunday, Obama said that the outcome of the Syrian deal on its chemical weapons arsenal offered Iran a "lesson" in the benefits of diplomacy, but warned Tehran over its nuclear programme.
"My suspicion is that the Iranians recognise they shouldn't draw a lesson -- that we haven't struck (Syria) -- to think we won't strike Iran," he said.
Obama said that the nuclear issue was "far larger" for the US than chemical weapons.
"The threat against ... Israel, that a nuclear Iran poses, is much closer to our core interests," he said, adding that a nuclear arms race in the region would be "profoundly destabilising".
Western countries and Israel accuse Iran of trying to develop and build nuclear weapons under cover of its nuclear energy programme, an allegation that Tehran has repeatedly denied.
Iran and the Western powers are due to relaunch nuclear negotiations before the end of September at a meeting in New York on the sidelines of the United Nations General Assembly.
In the ABC interview, Obama also revealed that he and Iranian President Hassan Rowhani had exchanged letters.
Afkham on Tuesday confirmed that an exchange of letters "through diplomatic channels" had taken place, saying that Obama had congratulated Rowhani on his election. Rowhani, in turn, "thanked (Obama) while clarifying some points," Afkham said without elaborating.
She also added that no meeting was scheduled between Rowhani and US or British officials on the margins of the UN General Assembly meeting next week.
Iran's Foreign Minister Mohammad Javad Zarif, who is responsible for nuclear negotiations, is due to hold talks with his European counterparts, including EU foreign policy chief Catherine Ashton.
"I am leaving this evening for New York, I am going to have meeting with certain foreign affairs ministers, Ms Ashton and probably with the 5+1," Zarif said on his Facebook page, referring to the group that comprises the five permanent UN Security Council members and Germany.