Danish shipping company Torm said one of its tankers was attacked by suspected pirates in the Gulf Of Guinea on Saturday, but the 20-strong crew was reported unharmed.

The crew of the Torm Alexandra, which was sailing off the coast of Benin, saw suspected pirates approach the 183-metres long vessel and took refuge in a designated security room, Torm spokesman Joakim Norholm Vasehus told dpa.

It was not known whether the suspected pirates were still on board and the crew, comprising 19 Filipinos and one person from Montenegro, was still in the security room, Vasehus said.

The tanker left Lome in Togo on Friday and was heading for Libreville, Gabon. Torm's fleet is specialized in carrying refined oil products.

Maritime piracy and armed robbery are a recurring threat to ships in the Gulf of Guinea.