The fleet oiler USS John Lenthall is seen in a handout photo. REUTERS/DefenseImagery.mil/Handout

LONDON (Reuters) - The U.S. Navy said on Wednesday it appeared pirates had tried to attack one of its big military oil tankers.

A security team aboard the vessel opened fire on two small boats near Somalia after they ignored warnings and pursued the ship, a U.S. Fifth Fleet spokesman said.

“From all appearances it does look like it was a pirate attack and the incident is currently under investigation,” he said by telephone from Bahrain.

He said the Military Sealift Command (MSC) oil tanker, the John Lenthall, which usually carries a range of fuels for the U.S. armed forces, was transiting outside Somalia’s territorial waters when the incident took place.

In a statement the navy said a whole range of warnings were given before the security team opened fire on the small open skiffs which came within 400 yards of the tanker.

The skiffs then retreated and the navy said there were no reports of any casualties.

“This incident is clear proof that all mariners must remain vigilant,” said Captain Steve Kelley, the commander responsible MSC ships in the region.

Somali pirates have in the past mounted attacks on merchant shipping from skiffs launched from so-called “mother ships” in the waters in and beyond Somalia.

Heavily armed Somali pirates have hijacked more than 30 merchant vessels of the Horn of Africa country this year, with attacks off its coast and the Gulf of Aden almost every day.