OSLO (Reuters) - The number and scope of pirate attacks is seen increasing worldwide and could trigger more joint military operations to keep shipping lanes safe, a top NATO official said.

Commodore Hans Christian Helseth said attacks around the Horn of Africa will become more frequent in the coming months due to less stormy weather and likely spread further east towards India and south towards Madagascar.

Pirate attacks risk maritime trade, which accounts for 90 percent of global trade volume. Last year piracy hit its highest level since 2003, with Somali gangs accounting for more than half the 406 worldwide incidents.

"We have now a three-month period between the winter and summer monsoons and in this period pirates are departing (more often) with fuel and supply to give them considerable range into the Indian Ocean," Helseth told Reuters on the sidelines of a seminar on piracy in the Norwegian capital.

"During the monsoons the seas are rougher ... It is tough for these small vessels to deal with two-metre waves," he said.

Helseth is Deputy Chief-of-Staff of Operations at NATO's Allied Maritime Command at Northwood, near London, and a leader of operation Ocean Shield — the North Atlantic military alliance's counter-piracy activities in the Indian Ocean.

Aside from NATO, the European Union, India, China and the US-led Combined Maritime Forces (CMF), among others, are also conducting anti-piracy operations in this region.

Coordinating these efforts could lead to some unusual multinational reporting lines, he said.

"By the end of 2010 US warships could be coordinated by a Chinese admiral," Helseth told the piracy seminar.

He said there was pirate activity in the Bay of Bengal near Bangladesh as well as in the Gulf of Guinea off Nigeria.

Asked whether counter-piracy operations could be conducted in the Gulf of Guinea, Helseth said: "It is conceivable ... It's an important area for energy deliveries" but added that he had not heard of such discussions within NATO.

The threat of piracy has lessened in the Gulf of Aden, a busy shipping lane between the Arabian peninsula and the Horn of Africa that leads to the Suez Canal, but remained high in the Somalia Basin region off eastern Africa, he said.

"The corridor (in the Gulf of Aden) is always priority number one, but everything that can be spared from that operation we send to the Somalia Basin," said Helseth.

"The threat level in the Gulf of Aden will always remain there in the background, but I think we have managed to suppress the problem to the lowest level it possibly can be."

Helseth said that up to 30 percent of ships did not follow recommended safety precautions, such as avoiding areas where attacks were more frequent, if it meant higher transport costs.

"For some owners, only the profit matters, they don't care about the crew's safety," he said, adding that attacks can be avoided if ships use lookouts, surround decks with barbed wire and water hoses to sink incoming pirate boats, or sail in rougher seas and at higher speeds.