President Donald Trump says Tehran has "no plan" to execute protesters, but still hasn't ruled out US military action against the country over its violent crackdown on anti-government demonstrators.
The US and UK are both reducing the number of personnel at the Al-Udeid air base in Qatar, while officials have told CBS, the BBC's US partner, that a partial American withdrawal is a "precautionary measure".
Iran's airspace was closed to nearly all flights for five hours overnight, with several airlines announcing that they will reroute flights around Iran.
The Foreign Office has also temporarily closed the British embassy in Tehran, which will now operate remotely, a government spokesperson said.
Speaking from the White House on Wednesday, Trump said his administration had been told "on good authority" that "the killing in Iran is stopping, and there's no plan for executions".
