A prosecutor in Benin said authorities had detained on Wednesday five Niger nationals for allegedly entering Benin's Seme-Kpodji pipeline terminal under false pretences, deepening a dispute over exports of crude oil from Niger via Benin.

In a statement on Thursday, special prosecutor Mario Metonou said the group had entered the terminal clandestinely and accused at least two of the detainees of being agents of Niger's ruling military junta.

"Investigations are ongoing to determine the real motives ... in a context where recurring information suggests the planning of acts against the security of the state of Benin," Metonou said.

On Thursday, Niger's Oil Minister Mahamane Moustapha Barke Bako rejected the prosecutor's allegations, telling a press conference in Niamey that those arrested were inspectors supervising the loading of crude oil in line with an agreement with Benin.

Relations between the West African neighbours have been strained since Benin blocked crude exports via its port from landlocked Niger in May, demanding the junta reopen its border to Benin's goods and normalise relations before shipments can restart.

On May 15, Benin provisionally reversed the export block and agreed to hold a meeting between the two countries, but a long-term solution has not yet been agreed.

At the Niamey press conference, Nigerien Justice Minister said they would refer the issue to the arbitration court of the Organization for the Harmonization of Business Law in Africa.

The tensions go back to the July 2023 coup in Niger, which led the regional bloc ECOWAS to impose strict sanctions for more than six months.

Trade flows in the region were expected to normalise after the bloc lifted sanctions, but Niger has kept its borders closed to goods from Benin.