"As part of an agreement with Iran to resolve safeguards implementation issues specified by the IAEA, the agency this week conducted a complementary access at the second location in the country and took environmental samples," the International Atomic Energy Agency said in a statement.

Late last month Iran announced it would allow the IAEA access to two sites -- their exact locations have not been made public -- following a visit to Tehran by IAEA Director General Rafael Grossi.

The first site was visited by inspectors in early September.

Iran had denied the agency access to the locations earlier this year, prompting the IAEA's board of governors to pass a resolution in June urging Iran to comply with its requests.

The row had threatened to put yet more strain on the 2015 landmark Iran nuclear deal, which has hung by a thread since the US pulled out of it in 2018.

At a press conference on September 14, Grossi said analysing environmental samples collected at the first site would take "not less than a couple of months, two or three months maybe".

On Wednesday the spokesperson for the Iranian Atomic Agency Organization, Behrouz Kamalvandi, confirmed that the second site inspection had taken place and said access to the two sites had been given "on the condition that they not be raised again".

Referring to the agreement struck while Grossi was in Tehran, Kamalvandi said: "There was a possibility of America exploiting this issue, therefore by inviting the agency's director we talked about our concerns."

"We hope that such visits would deprive America of the excuse they sought for politicising Iran's case and bringing it to the Security Council," Kamalvandi told the Akharin Khabar news agency.