An unidentified gunman riding a motorcycle shot and killed an American oil worker Wednesday in a southern Nigeria city, police said.

Police Commissioner Samuel Adetuyi said the American worked for the U.S. drilling equipment maker Baker Hughes Inc. and was riding in a car to his Port Harcourt office when the unknown assailant shot him.

Adetuyi had no further details.

The U.S. Embassy said it was investigating the report. It was not immediately possible to reach company officials for comment.

A new militant movement whose attacks on oil installations have cut more than 20 percent of Nigeria's of 2.5 million daily barrel production said Tuesday it would target oil workers with fresh attacks.

It was not clear if Wednesday's killing was linked to the threat from the Movement for the Emancipation of the Niger Delta. A movement spokesman couldn't be reached for comment.

The Movement for the Emancipation of the Niger Delta says it is fighting for local control of oil revenues by the impoverished inhabitants of the oil-producing delta who feel cheated out of the wealth produced in their backyards.

The group has kidnapped American and other foreign oil workers, but released them later unharmed.