(Photo: CGTN)

Iran has followed through on a threat to accelerate its production of enriched uranium, the head of the UN atomic watchdog said on Monday, departing from his usual guarded language to say he was worried about increasing tension.

Recent weeks have seen US-Iranian confrontation sharply increase, a year after Washington abandoned an agreement between Iran and world powers to curb Tehran's nuclear program in exchange for the lifting of international financial sanctions.

Washington tightened sanctions from the start of May, ordering all countries and companies to halt all imports of Iranian oil or be banished from the global financial system.

It has also begun discussing military confrontation, dispatching extra troops to the region to counter what it describes as Iranian threats.

Iran has responded with a threat to increase its enrichment of uranium, saying it was up to Europeans who still support the nuclear deal to save it by finding ways to ensure Tehran receives the economic benefits it was promised.

IAEA chief Yukiya Amano, whose agency is responsible for monitoring Iranian compliance with the nuclear deal, said Iran is now producing more enriched uranium than before, but it was not clear when it might reach stockpile limits set in the pact.

"Yes, [the] production rate is increasing," he told a news conference when asked if enriched uranium production had accelerated since the agency's last quarterly report, which found Iran compliant with the nuclear deal as of May 20. He declined to say how much it had increased by.

Iran said last month it was still abiding by the deal but would quadruple its production of enriched uranium – a move that could take it out of compliance if stockpiles rise too far. It demanded European countries do more to shield it from sanctions.

On Monday, Germany's Foreign Minister Heiko Maas became the most senior Western official to visit Iran since the new war of words erupted last month between Washington and Tehran.

"The situation in the region here is highly explosive and extremely serious," Maas told a news conference alongside Iran's Foreign Minister Mohammad Javad Zarif. "A dangerous escalation of existing tensions can also lead to a military escalation."

Zarif blamed the United States for the escalation. 

"Reducing tension is only possible through stopping the economic war by America," he said. "Those who wage such wars cannot expect to remain safe."

Zarif said talks with Maas were "frank and serious". 

But he added: "Tehran will cooperate with EU signatories of the deal to save it."