The International Maritime Bureau, which monitors the world's shipping, says there have been more than 300 attacks or attempted attacks by pirates so far this year, a 25 percent increase over the same period last year.

The deputy director of the IMB, Jayant Abhyankar, says the situation in Southeast Asia is especially worrying. He highlights a recent wave of attacks that targeted three petroleum tankers over the course of four days in the Malacca Straights, the narrow waterway between Indonesia and Malaysia through which hundreds of ships pass every day.

"In July this year we had a liquefied natural gas carrier, a gas carrier and an oil tanker being fired at by pirates," he said. "That itself causes immense concern from an environmental point of view."

He says the rise in attacks in the straights could be due to political unrest in nearby Aceh and Sulawesi, both provinces of Indonesia. The country's waters are the most pirate-infested in the world.

Captain Abhyankar says the number of violent attacks has risen by more than 15 percent in the past year. The number of crewmembers killed, mostly in the Philippines and Bangladesh, has more than tripled to 20 so far this year from six last year.

Few pirates have been arrested, he says, and this is the fault of local law officials.

"Unless they catch these guys and punish them, prosecute them, the problem is not going to go away," said Captain Abhyankar. "After all, these guys have to come ashore with their loot and that's where the normal law enforcement will apply and they can be caught and tried."

Captain Abhyankar notes some countries, namely Thailand and Malaysia, have made progress in reducing piracy in their waters. But he says Indonesia, Bangladesh, the Philippines and Nigeria continue to experience a high number of attacks.