More than two dozen Indonesian and Malaysian crewmen have been kidnapped by Abu Sayyaf militants and their allies since April

The US military is concerned about a series of attacks and abductions of tugboat crewmen by Abu Sayyaf extremists in south-east Asian waters and is willing to lend a hand if needed, aiming to ensure the freedom and safety of navigation in the region, a US navy official said Monday.

Rear AdmBrian Hurley said the navy has worked with south-east Asian governments to ensure freedom of navigation and the safety of people in the economically bustling region and would continue to do so.

Indonesia, Malaysia and the Philippines have agreed to take possible coordinated actions, including sea and air patrols, and establish a “transit corridor” as designated sea lanes for boats and ships in the seas along their borders, in an attempt to stop an alarming wave of attacks by Abu Sayyaf extremists and allied militants.

More than two dozen Indonesian and Malaysian crewmen have been kidnapped by ransom-seeking Abu Sayyaf militants and allied gunmen who have used powerful speedboats to stage four attacks on slow-moving tugboats in the Sulu Sea and outlying waters since April.

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All the hostages from the first three attacks have been freed, reportedly in exchange for ransom, but a fourth tugboat came under attack last month and seven Indonesian crewmen were kidnapped, officials said.

A Philippine military officer, who has monitored the offshore attacks, said Abu Sayyaf may have been working with militants and contacts in Indonesia and Malaysia to carry out attacks on passing tugboats and commercial ships similar to the piracy assaults in Somalia few years ago.

The shift to piracy may have been prompted by stronger military actions that have made it more difficult for the militants to carry out kidnappings for ransom – a key source of funds by the Abu Sayyaf, the officer said.

“We are always concerned about safety at sea and the freedom of navigation through the waters,” Hurley said.

“From the navy’s perspective, it’s freedom of navigation through all these different straits – that we are doing that and working together in a multilateral engagement is very much appreciated and we will continue to do so.”

In the disputed South China Sea, the US navy deploys about 700 ships each year for patrols – an average of two ships per day – to ensure freedom of navigation “and we’ll continue to do that all over the world”, Hurley said.

Hurley and navy officials from Australia and New Zealand spoke on board the navy hospital ship USNS Mercy off Legazpi city in the north-eastern Philippine province of Albay, while participating in an annual humanitarian mission called the Pacific Partnership, which also aims to improve disaster preparedness.

More than 600 military and civilian personnel from the US, Australia, New Zealand, Canada, the UK, Malaysia, Singapore and South Korea are involved in the civic mission that was conceived following the December 2004 earthquake off Indonesia that triggered a tsunami that killed 230,000 people in a dozen countries.