Niger has been slapped with more sanctions, hours after its new military leaders rejected the latest diplomatic mission aimed at restoring constitutional order following a July 26 coup.

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 destabilise 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. US 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.

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

ECOWAS heads of state are preparing for a summit on Thursday to discuss their standoff with the junta, which defied an August 6 deadline to reinstate ousted President Mohamed Bazoum.

ECOWAS defence chiefs agreed last week on a possible military action plan, which the heads of state are expected to consider at their summit in the Nigerian capital, Abuja.

Still, Tinubu’s spokesperson said the leaders prefer a diplomatic solution.

“No options have been taken off the table,” the spokesperson told reporters in Abuja, adding that “far-reaching decisions” would be taken at the summit concerning the bloc’s next steps.

Explaining the decision to not allow the delegation in on Tuesday, Niger’s junta said it could not guarantee their safety in the face of popular anger. It also denounced “a climate of threatened aggression against Niger”.

The junta had already snubbed meetings with a senior US envoy and another ECOWAS delegation.

Under Bazoum, Niger was relatively successful in containing an Islamist insurgency in the Sahel region and was an important ally for the West after two of its neighbours rejected former colonial power France and turned towards Russia instead.

The UN said Secretary General Antonio Guterres strongly supported mediation efforts by ECOWAS, while US Secretary of State Antony Blinken told French radio station RFI diplomacy was the best way to resolve the situation.

Blinken later told the BBC he was worried that Russia’s Wagner Group mercenaries could take advantage of the instability in Niger to strengthen their presence in the Sahel.

“I think what happened and what continues to happen in Niger was not instigated by Russia or by Wagner, but to the extent that they try to take advantage of it – and we see a repeat of what’s happened in other countries, where they’ve brought nothing but bad things in their wake – that wouldn’t be good,” he said.

Adding to its strategic importance, Niger is the world’s seventh-biggest producer of uranium, the most widely used fuel for nuclear energy.