Iran urged the United States on Monday to address the Islamic Republic with respect, not threats of war, a day after US President Donald Trump stoked concerns about a potential US-Iran conflict.

But in a sign of brewing confrontation a year after Washington quit world powers’ 2015 nuclear deal with Iran and reimposed sanctions on it, Tehran announced a four-fold increase in its rate of low-grade uranium enrichment.

Tensions between Washington and its Sunni Arab allies on one side and Tehran and its Shia proxies in the region on the other have been flaring for weeks.

On Sunday, Trump tweeted: “If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!”

Iranian foreign minister Mohammad Javad Zarif replied on his twitter account, “NeverThreatenAnIranian. Try respect, it works!”

Zarif, who was educated in the US, actually praised Trump for earlier remarks seen as cautioning hawks in his administration who were encouraging conflict.

The President “rightly deplores ‘military-industrial complex’ pushing US #ForeverWars”, Zarif wrote on Twitter.

But he said Trump had allowed a “B-team” of aides led by National Security Advisor John Bolton to “trash diplomacy”. He accused them of “milking despotic butchers via massive arms sales”, an apparent reference to Iran’s main regional foe, Saudi Arabia.

Trump has tightened economic sanctions against Iran, and his administration says it has built up the US military presence in the region. It accuses Iran of posing threats to US troops and interests. Tehran has denied this, describing US moves as “psychological warfare”.

Britain told Iran on Monday not to underestimate the resolve of the US, warning that if American interests were attacked then the Trump administration would retaliate.

The foreign minister of Oman, a Gulf Arab state that in the past helped pave the way for negotiations between Iran and the US, visited Tehran on Monday. Yousuf bin Alawi bin Abdullah addressed regional and international issues with Zarif, Iranian state news agency Irna said, without elaborating.

Quoting an official at the Natanz enrichment plant, the semi-official Tasnim said Iran was accelerating the rate at which it refines uranium to 3.67 per cent fissile purity, suitable for civilian nuclear power generation.

The move came after Iran, acting after Trump reimposed sanctions, declared it would scale back some commitments under the accord it signed with six world powers. Reuters