Benin has eased trade restrictions on its side of the Niger border, after sanctions were imposed on Niger following a coup in July last year.
But Benin President Patrice Talon has for weeks complained that Niger's rulers were not cooperating to restore ties and formally normalize trade.
"The Nigerien authorities must officially say that oil is exempted from the closing of their land border," he said, adding that this would "allow a different statutory treatment for oil coming from Niger."
"Without this minimal step, all oil custom formalities are impossible between Benin and Niger."
Landlocked Niger runs a pipeline from its oilfields to Benin's Seme port on the Atlantic coast to export its crude.
The Benin president has been pushing for the military rulers to formally normalize trade, rather than allow informal border crossings.
"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," he said in a statement in early May.
Benin had already announced it would reopen its border, but Niger's military rulers have so far kept their side of the frontier closed.
The closure of Benin's 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 Niger following the coup in Niamey.
Niger — one of the world's poorest countries— has been able to sell crude on the international market for the first time via Seme.
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