The Iranian mission to the United Nations denied "direct contact" between Iranian and American officials adding: "No such contacts have occurred," the ISNA and Fars news agencies reported.
"There are no such contacts, and this office has no information in this regard," local media added, quoting a statement by the Iranian mission.
On Thursday, State Department spokeswoman Victoria Nuland told reporters that Washington had "had direct contact with Iran," when asked about communication between the two sides, adding that this took place on Wednesday and not in Iran.
A senior US State Department official told reporters later that the contact took place at the US initiative.
US President Barack Obama demanded answers from the top echelons of the Iranian government over the alleged plot and said the facts of the plan were not in dispute.
Iranian supreme leader Ayatollah Ali Khamenei, in a speech Thursday that appeared to be prompted by, but did not directly address, US allegations of a thwarted Tehran-sponsored plot, said the West is trying but failing to instil "Iranophobia."
"The repeat of ineffective and stupid methods by hapless and distracted policy makers in the West (to spread) Iranophobia will again bear no result," he said.
Iran has strongly denied any involvement in what the US says was a plot by the Iranian Revolutionary Guards' elite Quds force to kill the Saudi ambassador by hiring assassins from a Mexican drug cartel for $1.5 million.
News of the alleged plot 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.