LONDON - The British Royal Navy captured 13 Somali pirates in the Indian Ocean on Friday, Defence Ministry said.

A British Royal Fleet Auxiliary (RFA) supply ship and a US Navy vessel intercepted the pirates' boat, which refused to stop despite warning shots fired from a British helicopter.

The British navy then sent commandos to board the boat, capturing the 13 pirates and seizing their weapons.

Defence Secretary Philip Hammond said the British troops, part of a NATO-led counter-piracy force, could be "proud" of the success.

Captain Gerry Northwood, who leads the operation, said the capture will "send a clear message to other Somali pirates that we will not tolerate their attacks on international shipping."

Earlier this week, the same British ship, RFA Fort Victoria, foiled an attempt by Somali pirates to attack cargo ships in the Indian Ocean, the Defence Ministry added.

In the operation on Tuesday, the British navy blocked the pirates' attempt to sail the hijacked tanker Liquid Velvet from the Somali coast into the Gulf of Aden where they would have used it as a mother ship to attack passing ships.

Fort Victoria "cut off Liquid Velvet's progress after she had sailed 90 miles (145km) from the coastline, forcing her to return to Somalia", the Defence Ministry said.

The Greek-owned chemical tanker Liquid Velvet had been held to ransom since last November.