Pirates attacked a British-flagged oil tanker off the coast of Yemen Sunday, causing some minor damage but no injuries.

Operators of the Stolt Apel say six gunmen in two separate speedboats sped toward the tanker about 140 kilometers off Yemen in the Gulf of Aden.

Armed guards aboard the boat returned fire, disabling one of the speedboats.

A spokesman for Stolt Tankers says their vessel suffered only minor damage and no one on board was hurt. No leaks from the tanker are reported.

It is unclear if any of the pirates were hurt or where they were from.

Maritime security experts say this was the ninth incident of piracy at sea in the Gulf of Aden this year.