As the United States continues a significant military buildup in the Middle East, Iran has taken steps to signal its readiness for war, including fortifying its nuclear sites and rebuilding missile production facilities.

President Trump has one bright red line for Iran's nuclear program and some areas of flexibility as he weighs military strikes or a possible deal in the coming days.

U.S. President Donald Trump, who scrapped an earlier nuclear agreement with Iran during his first term, has repeatedly threatened to use force to compel Iran to agree to constrain its nuclear program. Iran has said it would respond with an attack of its own. Trump has also threatened Iran over the killing of protesters.

There have already been confrontations between the US military and Iranian forces. The US this month shot down a Shahed drone that approached the Abraham Lincoln carrier. On the same day, members of Iran’s Islamic Revolutionary Guard Corps threatened to board and seize a US-flagged tanker, prompting a US destroyer to respond.

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

Rarely in modern times has the United States prepared to conduct a major act of war with so little explanation or public debate.

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.

Although the United States and ally Israel have a military advantage over Iranian forces, there are ways for Tehran to make any attack painful, officials said.

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.