Nigerian President Bola Tinubu ordered the new sanctions through Nigeria's central bank, aimed at squeezing those involved in the takeover, a presidential spokesperson said.

The sanctions were imposed after the junta denied a joint delegation from West African states, the African Union (AU) and the United Nations permission to enter Niger, resisting pressure from the United States and the UN to come to the negotiating table.

Late on Tuesday, the Economic Community of West African States (ECOWAS) confirmed the joint mission had been aborted and said in a statement it would "continue to deploy all measures in order to restore constitutional order in Niger."

Regional and Western powers fear the coup will destabilize the Sahel region of West Africa, one of the world's poorest that is already dealing with a string of coups and a deadly Islamist insurgency.

Border and airspace closures have cut off supplies of medicine and food, hampering UN humanitarian aid. U.S. and Western interests in Niger, a former ally, are also under threat.

"We are still hopeful and we are still trying to achieve a result that is a return to the constitutional order," US State Department spokesperson Matthew Miller told reporters on Tuesday.

Funding for international military education and training, peacekeeping operations, and foreign military financing programs supporting Niger's counterterrorism capabilities are among the assistance the U.S. has paused since the coup, he said.