Rafael Mariano Grossi, on his first trip to Iran since taking the helm of the International Atomic Energy Agency last year, is to meet with senior officials on Tuesday.

He is expected to press for IAEA access to two nuclear sites in the talks with Foreign Minister Mohammad Javad Zarif and the head of the country's atomic agency, Ali Akbar Salehi.

"My objective is that my meetings in Tehran will lead to concrete progress in addressing the outstanding questions that the agency has related to safeguards in Iran and, in particular, to resolve the issue of access," Grossi said in a statement on Saturday.

The visit comes amid tensions between the US and its European allies over Washington's bid to maintain an arms embargo on Iran and reimpose UN sanctions dating back to 2006.

His visit also takes place shortly before a September 1 meeting of the joint commission on the 2015 deal between Iran and global powers, which aims to prevent Tehran from developing a nuclear bomb.

Tehran has always denied its nuclear programme has any military dimension.

The US and European nations are at loggerheads after Washington began the process Thursday of activating a controversial mechanism aimed at restoring UN sanctions against Iran.

Britain, France and Germany rejected the move, saying it frustrated their efforts to salvage the 2015 nuclear accord that US President Donald Trump pulled out of two years ago.

Washington controversially maintains it has the right to force the reimposition of sanctions through the agreement's "snapback" mechanism, despite its withdrawal.

Iran-US tensions have escalated since the US in May 2018 withdrew from the deal formally known as the Joint Comprehensive Plan of Action, or JCPOA.

In retaliation, Iran has progressively abandoned commitments under the accord that was meant to give it relief from sanctions in exchange for curbs on its nuclear programme.

Grossi is also expected to meet Iran's President Hassan Rouhani on Wednesday before flying back to Vienna, where the UN agency is based.

Iran had expressed hopes that the Argentine would act "neutrally" after his appointment in July last year following the death of his predecessor, Japan's Yukiya Amano.