Iran said on Saturday that the US government rebuffed its request to hand over information on an alleged Iranian plot to kill the Saudi ambassador to Washington.
"This person has had no link to Islamic Republic of Iran entities," the foreign ministry said in a statement received by AFP, referring to a suspect named by the United States.
"Based on legal norms, if there is any claim against any other government, the US government should submit the accused person's information to the other country and request cooperation," it said.
"The US government, despite a clear request from the Islamic Republic of Iran and contrary to international conventions, has not taken any action in this regard," the ministry added.
The statement came a day after conflicting reports from Tehran and its arch-foe, Washington, over contacts.
Local media reported Friday that Iran's mission to the United Nations denied "direct contact" between Iranian and American officials, after State Department spokeswoman Victoria Nuland told reporters that Washington and Tehran had had such contact over the alleged plot.
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Nuland later insisted Washington had direct contact with Tehran.
Iran has strongly denied any involvement in what the US says was a plot by the Iranian Revolutionary Guards' elite Quds force to kill Adel al-Jubeir, possibly through the bombing of a Washington restaurant by hiring assassins from a Mexican drug cartel.
News of the alleged plot which surfaced on Tuesday has sent tensions soaring between Tehran and Washington, foes for more than 30 years ever since Islamic students took US diplomats hostage in their embassy in Tehran after Iran's 1979 revolution.
An Iranian used-car salesman who is a naturalised US citizen living in Texas, Manssor Arbabsiar, is said to have confessed to acting as the go-between for his cousin, whom he described as a high-ranking official in the Quds Force, and the Mexican cartel.
Arbabsiar is in US custody, charged with the plot.
The US Justice Department has also charged another Iranian identified as Gholam Shakuri, who is said to be an Iran-based Quds Force operative who flew to the United States to speak with Ababsiar. He is now believed to be in Iran.