President Mohamed Bazoum, who says he is a "hostage", has been living without electricity and running water, and only has rice and canned goods left to eat after mutinous soldiers moved against him on 26 July, according to the source.

The leader is being held in the presidential palace in the country's capital with his wife and son.

He remains in good health for now, and according to the adviser, will never resign from his position.

US Secretary of State Antony Blinken spoke with the leader on Tuesday and "emphasised that the safety and security of President Bazoum and his family are paramount," a spokesperson said.

It comes after civilian economist Ali Mahaman Lamine Zeine was named as Niger's new prime minister by the junta on Monday, while the head of the presidential guard, General Abdourahmane Tchiani, claims he now runs the country.

The new military regime has also closed Niger's airspace until further notice, citing the "threat of military intervention" from the West African regional bloc (ECOWAS), after coup leaders rejected Sunday's deadline to reinstate President Bazoum.

Thousands of junta supporters flocked to a stadium in Niamey, the country's capital, to cheer the decision not to bow to external pressure to stand down.

ECOWAS had threatened to use military force if the deadline was ignored. Members of the bloc are expected to meet on Thursday to discuss the situation.

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Niger's 25 million-strong population is also bearing the brunt of the coup.

As one of the poorest countries in the world, many have said they are too focused on finding food for their families to pay much attention to the escalating crisis.

Erkmann Tchibozo, a shop owner, said it's been hard to get anything into the country to stock his business near the airport.

The junta claims they can do a better job at protecting Niger from jihadi violence and groups linked to al Qaeda and IS, which have ravaged the Sahel region.

Neighbouring Mali and Burkina Faso, both of which are run by military regimes, have sided with the junta and warned an intervention in Niger would be "tantamount to a declaration of war" against them.

Both countries sent representatives to Niamey this week to discuss military options, while other African nations remain divided on how to proceed.