Sri Lanka Monday called for tougher action against Somali pirates operating in the Indian Ocean and said multinational efforts had so far proved insufficient to deal with the threat.

Top defence official Gotabhaya Rajapakse asked maritime powers to share intelligence and ensure joint and coordinated patrols in a region which accounts for more than 50 per cent of the world's container cargo traffic.

"Existing international maritime laws and practices have proven ineffective in combating the activities of the Somali pirates," Rajapakse said at a regional conference on maritime security organised by Sri Lanka's navy.

His remarks came after Maldivian President Mohamed Nasheed announced Friday that his atoll nation was working with Sri Lanka and India to work out a strategy to deal with Somali pirates.

Nasheed said they had arrested 37 Somali pirates who were drifting near the Maldivian archipelago, but lamented that they lacked laws to deal with them as they appeared to be unarmed at the time they were detained.

"By the time they drift towards our coasts, they have thrown their weapons and ammunition overboard and pretend to be refugees," Nasheed told reporters after a South Asian summit in the Maldives.

Rajapakse said Sri Lanka too had arrested an unspecified number of Somali pirates.

"It is clear that the activities of the pirates are spreading at a rapid pace. Thousands of people have been affected by their attacks over the last several years," Rajapakse said.

He added that the cost to international shipping from piracy was close to $10 billion a year.

"It is our belief that the lasting solution to threats of this nature cannot be undertaken by individual nations in isolation, but only through greater international cooperation," he added.

US deputy assistant secretary of defence for South and Southeast Asian Affairs Robert M. Scher said Washington was looking at an increased role in the Indian Ocean to ensure global security and stability.

"I would like to reiterate that the US is increasingly attuned to the strategic importance of the Indian Ocean region, not only to our own national defence and economic security, but to global security and stability," he told the conference.

Two decades of lawlessness have carved up Somalia into mini-fiefdoms ruled by gunmen and militia, encouraging rampant piracy.

At least 47 foreign vessels and more than 500 sailors are being held by pirates, according to Ecoterra International, which monitors maritime activity in the region. (Source: AFP)