The UN's nuclear watchdog chief revealed on Monday that Iran has accelerated its production of enriched uranium, as Tehran warned the US it "cannot expect to stay safe" after introducing sanctions on the country. Yukiya Amano, director general of the International Atomic Energy Agency (IAEA), voiced rare concern over "increasing tensions" between Washington and the Islamic Republic. He said Tehran was now producing more enriched uranium than before, following through with a threat made last month. Iran announced in early May that it no longer considered itself bound to keep to the limits of stocks of heavy water and enriched uranium which were agreed as part of the 2015 landmark nuclear deal, after the US withdrew. "Yes, (the) production rate is increasing," Mr Amano 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. Director General of the International Atomic Energy Agency, IAEA, Yukiya Amano of Japan, addresses the media during a news conference after a meeting of the board  Credit: AP He declined to say how much it had increased by and it was not clear when it might reach stockpile limits set in the pact. President Donald Trump pulled the US out of the multilateral accord, introduced sanctions on Tehran and has pressured allies to cut trade with the Islamic Republic, crippling the country's oil economy. During a meeting with his German counterpart in Tehran on Monday, Mohammed Javad Zarif, Iran's foreign minister, issued the stark warning over US security, accusing it of launching an “economic war” on his country. He said Iran would not start a war but “whoever starts a war with us will not be the one who finishes it”. President Donald Trump shows a signed Presidential Memorandum after delivering a statement on the Iran nuclear deal Credit: AP The visit by Heiko Maas was part of a concerted European effort to preserve the nuclear pact with world powers and defuse rising US-Iranian tensions. "The only way to decrease tensions in the region is to stop the economic war," Mr Zarif said, adding that Germany and the EU had an "important role" in such efforts. Iran has claimed the European signatories to the deal have not done enough to provide it with alternative ways to trade. Mr Maas acknowledged limits to how much help the European countries can provide. "We want to fulfil our obligations," he said during his joint news conference with Mr Zarif. "We cannot work miracles, but we will try to avert a failure." France, Britain and Germany have set up a special-purpose vehicle called Instex, designed to allow payments to Iran that would legally bypass sanctions but it is yet to be launched. "This is an instrument of a new kind, so it's not straightforward to operationalise it," Mr Maas told reporters. "But all the formal requirements are in place now, and so I'm assuming we'll be ready to use it in the foreseeable future."