Like Jonathan, Asari is from the Ijaw ethnic group. He is best known for staging attacks on oil infrastructure in the swampy creeks of OPEC member Nigeria that drove up oil prices to record highs in 2004.
"It was under pressure from the Nigerian head of state that the authorities freed the rebel chief on Friday at around midday," said Benjamin Agon, spokesman for Benin's foreign affairs department. Benin police declined to comment but Asari's lawyer Festus Kiyamou confirmed the release and said his client was now in the Nigerian capital Abuja.
There was no immediate comment from the Nigerian government on the case. Diplomats told Reuters this week that Cotonou had been investigating Asari's business interests in Benin, a tiny cotton producing country which borders oil giant Nigeria.
One of the diplomats said Asari's group, the Niger Delta People's Volunteer Force, had been suspected of lending support to criminal activities in the Delta.
Asari's Niger Delta People's Volunteer Force reached a peace deal with the Nigerian government in 2004.
However, oil production in the region is still frequently disrupted by criminal gangs who tap crude from pipelines for local refining or sell it onto large tankers for export.
