Mahmoud Ahmadinejad has dismissed accusations from Washington that Iranian government agents plotted to kill the Saudi ambassador in the United States.
"Iran is a civilised nation and doesn't need to resort to assassination," the Iranian president was quoted by the official IRNA news agency as saying. "Terror belongs to you," he said, addressing the United States.
Two men, including a member of Iran's special foreign actions unit known as the Quds Force, have been charged in New York's federal court with conspiring to kill Saudi diplomat Adel Al-Jubeir.
Iranian officials have consistently denied the allegations since they first emerged last week.
Ahmadinejad's statement, and similar remarks made on Saturday by Iran's supreme leader Ayatollah Ali Khamenei, are the first comments made on the issue by the country's two highest leaders.
Khamenei, who has the final say on all state matters in Iran, had said that the US seeks to bring greater pressure on Iran through making unsubstantiated allegations.
"They (Americans) conduct such conspiracies against us frequently, which are all useless and ineffective. They say that they want to isolate Iran but they have become isolated themselves," Khamenei said on state TV.
"By attributing an absurd and meaningless accusation to a few Iranians, they tried... to show that Iran is a supporter of terrorism... This conspiracy didn't work and won't work," he said.
US President Barack Obama said on Thursday that the US will be able to support all of its allegations that Iran was directly involved in a plot to kill Mr Al-Jubeir.
Later, Khamenei warned the United States that any measures taken against Tehran over the alleged plot would elicit a "resolute" response. "If US officials have some delusions, (they must) know that any unsuitable act, whether political or security, will meet a resolute response from the Iranian nation," state TV quoted Khamenei as saying.