France has detained a Lithuanian cargo ship suspected of causing a 37-kilometer long oil slick off France's northwestern coast.

The French navy escorted the ship, Vytautas, to the port of Brest, where an investigation is under way.

A French naval plane spotted the oil slick Monday and traced it to the Lithuanian vessel.

There has been no comment from Lithuanian authorities or the ship's crew.

Some information for this report was provided by AP and Reuters.