Iran on Thursday dismissed as "preposterous" claims that it was cleaning up its suspected nuclear military site at Parchin ahead of inspections agreed under a historic nuclear deal with world powers.

Iran's mission to the United Nations said in statement that "extensive construction work" was underway to repair a road near the Parchin complex but denied this amounted to a "hasty cover-up."

The statement was in response to media reports quoting US members of Congress who said the work at the military complex could complicate inspections by the UN nuclear watchdog IAEA that are a key provision of the deal.

"These claims are preposterous and the repetition of the similar unfounded claims that reappear from time to time and have been disproved each time," said the Iranian statement.

Iran argued that the Parchin military complex covers a "very, vast area" and that it was "quite normal to have construction works underway at any time."

Over the past week, a road near the Mamloo Dam, which is near Parchin, required repairs using heavy bulldozers and other heavy construction machinery, it added.

"We regret that the extensive vicious campaign at work, using tens of millions of dollars, to poison the positive environment at the global level, which followed the conclusion of the JCPOA" nuclear deal, the statement said.

Iran reiterated that it never engaged in nuclear military activity "that would need a hasty cover-up."

International Atomic Energy Agency director Yukiya Amano on Wednesday met lawmakers who are deeply skeptical of the deal that will lift sanctions on Iran in exchange for Tehran's commitment to curb its nuclear activities.

The nuclear deal has run into fierce opposition from Israel, which has friends on Capitol Hill.

US lawmakers will vote in September on whether to endorse the deal.