On Wednesday morning, one US government official thought there was a 90 per cent chance of the US declaring war on Iran within weeks.

Satellite images show that Iran has been reinforcing key military and nuclear facilities, including sites struck by the US and Israel last year, as possible war looms between Tehran and Washington. The hurried work has begun at several bases across Iran,

The NOTAM is issued for areas across southern Iran from 3:30 GMT to 13:30 GMT on Thursday.

Iranian officials promptly attributed the smoke to reeds catching fire along the adjacent riverbank, ruling out any building explosion. The Parand Fire Department reported that firefighters were on the scene tackling the flames,

Iran’s theocracy has faced down protests and U.S. threats in the past, and the crackdown showed the iron grip it holds over the country. This week, authorities organized pro-government rallies with hundreds of thousands of people to mark the anniversary of the 1979 Islamic Revolution.

Images also show Iran has buried tunnel entrances at a nuclear site bombed by the U.S. during Israel's 12-day war with Iran last year.

US Iran tensions highlights: Parand fire department told state media that the black smoke was due to a fire in the reeds around the Parand river bank.

A massive US military buildup in the Middle East suggests the US could be ready to launch a “sustained” bombing campaign on Iran in weeks — or even days — should Tehran continue refusing President Donald Trump’s demands in ongoing negotiations.