NATO is planning to deploy a new naval flotilla in the coming months to combat piracy off Somalia, the alliance said Thursday.

In November, NATO sent four warships to the waters off the Somali coast and the Gulf of Aden to stem a surge of pirate attacks against merchant shipping in one of the world's busiest sea lanes.

They were replaced in December by a European Union task force, which will remain in place until the end of 2009. A number of other countries, including China, Russia and India, also have contributed warships to the international effort to combat piracy.

Still, pirate attacks have continued, and NATO has been considering sending a follow-on force to reinforce it.

NATO Secretary-General Jaap de Hoop Scheffer told reporters that six vessels would be sent, although he did not say from which countries.

"It's a considerable strengthening of the anti-piracy role," he said. "We are seeing the end of the monsoon season, so I would not be astonished to see piracy go up again."

The U.N. Security Council has authorized countries to enter Somalia's territorial waters, with advance notice, and use "all necessary means" to stop piracy and armed robbery at sea.

The pirates are well-funded, well-organized and have easy access to heavy weapons in a country that has been in tatters for nearly two decades. Pirates travel in open skiffs with outboard engines, working with larger ships that tow them far out to sea. They use satellite navigational and communications equipment and have an intimate knowledge of local waters, clambering aboard commercial vessels with ladders and grappling hooks.

To date, pirates have raked in tens of millions in ransom and attacked and seized dozens of vessels carrying everything from palm oil and chemicals to luxury yachts. High-profile seizures include an oil tanker and a Ukrainian ship laden with tanks, both recently released.

Their focus has been the Gulf of Aden, between Somalia and Yemen, where 20,000 merchant ships a year pass on the way in and out of the Suez Canal, the quickest route from Asia to Europe and the Americas.