The U.S. Navy says a security team fired warning shots Wednesday at two small boats that tried to approach a naval supply ship off the coast of Somalia.   

USS Harry S. Truman, right, comes alongside the Military Sealift Command Oiler USNS John Lenthall for an underway replenishment in the Mediterranean (File Photo)

The Navy's Fifth Fleet says the shots were fired after a number of "defensive measures" were taken to deter the boats from approaching the USNS John Lenthall.

A naval statement says the shots landed about 50 meters from the closest boat and resulted in both small boats ending their pursuit.  There were no reported casualties.

Well-armed pirates, using powerful speedboats, have attacked more than 55 ships and private vessels through the Gulf of Aden and along Somalia's east coast this year.  

The United States and other countries have increased patrols and security in the area in an effort to protect the shipping lanes.

The international combined task force (CTF) said this week it has helped thwart more than a dozen attacks since its inception in August.  However, it warned that mariners must remain vigilant, adding that CTF patrols cannot guarantee safety in the region.

The Somali government is fighting an Islamist insurgency and lacks the power or resources to stop the hijackings.

Some information for this report was provided by AFP.