An American woman kidnapped by masked gunmen in central Nigeria last month was released on Friday and handed over to US government officials, police told AFP.

Phyllis Sortor, a missionary with the Free Methodist Church, was seized on February 23 in Kogi's Emiworo village.

"She has been rescued and given to the American authorities," Kogi state police spokesman Collins Sola Adebayo said, adding that no ransom was paid "as far as police are concerned."

An AFP journalist at the handover in Kogi's capital Lokoja said the 71-year-old Sortor appeared unharmed with no visible signs of abuse.

Her church confirmed the release but declined to provide details on the circumstances.

"As a matter of sound policy, and to help protect the many, many people who helped secure Phyllis' freedom, we will have no comment concerning the efforts that were undertaken to secure her release," Bishop David Kendall said in a statement.

Foreign nationals have often been kidnapped in Nigeria by local gangs who typically release hostages following a ransom payment.

Such abductions are especially common in the southern, oil-producing Niger Delta, where expatriates working with large oil companies have been a frequent target.

A number of foreigners have also been kidnapped in the north of the country, but those attacks claimed by Boko Haram or the associated Islamist group Ansaru are considered a different phenomenon, and not necessarily motivated by a desire for ransom.