President Patrice Talon on Wednesday demanded Niger's military rulers collaborate and reopen their side of the border if they want Benin to let ships load Nigerien crude exports at its Seme port.
Benin has eased trade restrictions on its side of the Niger border since sanctions were imposed on Niamey following a coup in July last year that ousted President Mohammed Bazoum.
But Talon said military leaders in its northern neighbour were treating Benin like an "enemy" and not cooperating to restore ties and formally normalise trade rather than allow informal border crossings.
Landlocked Niger runs a pipeline from its oilfields to Benin's Seme port on the Atlantic coast to export its crude.
"If you want to load your oil in our waters, you must consider that Benin is not an enemy country and that the territory of Benin cannot be the subject of illicit trafficking or informal exchange," Talon said in a declaration released by the presidency.
"If tomorrow the Nigerien authorities decide to collaborate with Benin in a formal manner, the boats will be loaded."
The Benin president did not directly state Niger's oil shipment loadings had been stopped or blocked.
In December, Benin lifted its suspension of imported goods transiting to Niger through the port of Cotonou, that had been part of sanctions imposed by the West African regional bloc ECOWAS following the coup.
The closure of its northern border with Niger hit Benin's government revenues and also impacted the cost of food goods.
Talon last year had been among the most vocal regional leaders calling for relations to be swiftly re-established between his country and neighbouring Niger.
Niger -- one of the world's poorest countries – has been able to sell crude on the international market for the first time via Seme port.