US Defence Secretary Mark Esper delivers a speech during a press conference in Paris. Christophe Ena/AP

The United Nations' nuclear watchdog says it has inspectors on the ground in Iran who will be able to look into reports that Tehran began injecting uranium gas into advanced centrifuges in violation of its 2015 nuclear deal with world powers.

The International Atomic Energy Agency told the media on Saturday it was aware of the reports "related to Iran's centrifuge research and development."

The Vienna-based IAEA says "agency inspectors are on the ground in Iran and they will report any relevant activities to IAEA headquarters."

Meantime, IAEA Acting Director General Cornel Feruta was traveling Saturday to Iran.

The agency said he will meet Sunday with high-ranking officials in Tehran as part of what it said were its "ongoing interactions" related to its monitoring under the nuclear deal. The IAEA, which issues compliance reports, meets in Vienna on Monday.

The US's top defence official has condemned Iran's latest breach of the terms of its nuclear deal with world powers, following Tehran's announcement it was using faster centrifuges.

In Paris, US Defence Secretary Mark Esper told reporters Saturday the Iranian moves should not surprise anyone.

At a news conference with his French counterpart, Florence Parly, Esper said: "It's no surprise that the Iranians are going to pursue what the Iranians have always intended to pursue."

Iran denies Washington's accusations that it seeks to develop a nuclear bomb, insisting its program is for peaceful purposes.

Parly said the focus should remain on keeping Iran in the 2015 deal. She said France "will continue to push in that direction."

The US unilaterally pulled out of the accord over a year ago.

Associated Press