China has been focusing on protecting its own shipping in the area, but it will now join the naval forces of the US, Nato and the European Union.

This grouping, the Shared Awareness and Deconfliction (Shade), protects a shipping corridor in the western Indian Ocean.

This is the area where pirate attacks are most frequent.

Members of the international naval task force say that although attacks there have increased, fewer have been successful.

Ransoms

The BBC's United Nations correspondent Barbara Plett says officials believe having China on board will allow more ships to be diverted to the Somali Basin, a vast expanse of water in the western part of the Indian Ocean, where attacks are at an all time high.

The agreement also allows China to take on the rotating chairmanship of the naval task force that coordinates patrols.

China is believed to be interested in raising its participation in the anti-piracy drive partly because one of its ships was hijacked last October.

The De Xin Hai bulk carrier was reportedly freed in late December amid reports of a possible ransom payment.

This is a positive step up of China as a responsible stake-holder
Prof Carl Thayer

Australian Defence Force Academy

Analysts say China is also eager to extend its naval reach beyond its shores.

Chinese media have reported the stepping up of China's role in anti-piracy patrols as the moment when China takes on a "central" and "leadership" role in an important international operation.

Hong Kong's South China Morning Post newspaper reported that China had been lobbying for the expanded role for months.

The newspaper editorialised that China would "show its worth as a global player".

Noting the concern, even alarm, among some of China's neighbours at the country's growth as a maritime power, the newspaper said China's participation in the anti-piracy effort would help increase trust.

South East Asian countries and China are rival claimants to islands and atolls across the South China Sea, and China's growing might and extended naval reach are being watched closely.