Tensions between Tehran and Washington have spiked since Thursday when an Iranian missile destroyed a United States, US, global hawk surveillance drone flying near the Iranian coast.

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

Under pressure to respond to the high-stakes incident near the strategic Strait of Hormuz, Trump said the United States, US, was prepared to hit "3 different sites" on Thursday night but that he scrapped the strikes "10 minutes" before they were to have been launched.

In an interview with NBC's "meet the press" at the white house on Friday morning, Trump said he had not given final approval to strikes against Iran, and that no planes were in the air.

The United States President had struck a combative tone in initial comments on Thursday about Iran shooting down the global hawk surveillance aircraft, but as the pre-dawn incident whipped up fears of open conflict, Trump moved to dial back tensions.

Iran vowed on Friday to defend its borders after downing the drone, with the commander of the aerospace arm of its elite revolutionary guard (IRGC) saying the aircraft was warned twice before it was engaged over the Gulf of Oman.