The head of the U.N. nuclear watchdog agency says Iran's enriched uranium "is still there," as he stresses the urgency of diplomacy to avert a U.S.-Iran war.

The U.S. has launched a major military buildup in the Middle East is it threatens Iran with potential military strikes.

US President Donald Trump delivered his latest ultimatum to Iran on Thursday during a meeting of the Board of Peace, the Middle East coalition Trump formed to stabilise a region he could soon plunge into a new, weeks-long war.

As Trump pressures Iran, he's spoken of an "armada" heading for the Mideast, but there's another massive movement of American fire power in the air.

What comes next would present its own set of challenges.

Defense expert Cameron Chell called Iran's military moves a "calculated escalation" as U.S. MQ-9 Reaper drones with strike capabilities were reportedly spotted in the region.

Iran has threatened to retaliate, including by striking U.S. bases, if Washington launches an attack on the country.