Trump Says He Blocked Iran Air Strikes To 'Spare Lives'

U.S. President Donald Trump says he aborted a military strike to retaliate for Iran's downing of an unmanned U.S. drone because it could have killed 150 people, and signalled he was open to talks with Tehran.

An Iranian surface-to-air missile destroyed a US Global Hawk surveillance drone on Thursday.

Tehran said the drone was shot down over its territory and Washington said it occurred in international airspace over the Strait of Hormuz.

Trump said he made an abrupt decision to cancel a planned attack on three sites.

READ MORE: Explained: America, Iran, And The 'Very Big Mistake' That Might Start War

Donald Trump
Photo: Getty Images.

In a series of early morning tweets on Friday, the president said he was in no hurry to launch a strike and that US economic sanctions designed to force Iran to curb its nuclear and missile programs and its involvement in regional wars were having an effect.

"We were cocked & loaded to retaliate last night," he said.

"Ten minutes before the strike I stopped it, not proportionate to shooting down an unmanned drone. I am in no hurry, our military is rebuilt, new, and ready to go, by far the best in the world," Trump tweeted.

White House national security adviser John Bolton, Secretary of State Mike Pompeo and CIA Director Gina Haspel, along with the rest of Trump's team, favoured a retaliatory strike, a senior Trump administration official said.

"There was complete unanimity amongst the president's advisers and DOD (Department of Defence) leadership on an appropriate response to Iran's activities. The president made the final decision," the official said.

Iranian sources told Reuters that Trump had warned Iran via Oman that a U.S. attack on Iran was imminent but said he was against war and wanted talks.

Washington also requested a closed-door UN Security Council meeting on Monday.

Trump's abrupt decision drew mixed reviews in Washington, with some people criticising him for flinching while others, notably senior Democrats, praising what they saw as restraint.

"A strike of that amount of collateral damage would be very provocative, and I'm glad the president did not take that," House of Representatives speaker Nancy Pelosi told reporters.

US President Donald Trump said Iran may have made a mistake in shooting down a drone. Photo: AAP.

However Michael Makovsky, a former Pentagon official and now head of the Jewish Institute for National Security of America (JINSA), a think tank that favours strong US-Israeli security ties, said Trump was undermining U.S. credibility.

"Trump has given the impression he lost his nerve," Makovsky said in a statement.

READ MORE: Trump Says Iran May Have Made 'A Very Big Mistake' In Shooting Down Drone

Iranian officials earlier told Reuters that Tehran had received a message from Trump warning that a U.S. attack on Iran was imminent but saying he was against war and wanted talks.

"He gave a short period of time to get our response but Iran's immediate response was that it is up to Supreme Leader (Ayatollah Ali) Khamenei to decide about this issue," one of the officials told Reuters, speaking on condition of anonymity.

Khamenei has the last say on all state matters and has ruled out any talks with Washington while Tehran is under sanctions.