By Kate McGeown
BBC News Online
A new brand of piracy is threatening commercial shipping in the Malacca Straits, amid allegations that rebels from the Indonesian province of Aceh are to blame.
According to the International Maritime Bureau (IMB), gangs of heavily armed men are increasingly targeting cargo ships, especially oil tankers.
But instead of stealing the goods as most pirates do, these gangs are kidnapping the crew and holding them to ransom.
The IMB's director, Captain Pottengal Mukundan, told BBC News Online that the attacks had all the hallmarks of the Free Aceh Movement (Gam), which the Indonesian Government is currently trying to crush in a military operation.
Gam has vehemently denied the IMB's claim.
"We not doing any piracy, because our organisation is campaigning for freedom," Gam spokesman Abu Safyan Daud told the BBC.
Pirates have long targeted the Malacca Straits, where more than 600 ships pass every day.
But over the last few months, the frequency of these attacks has increased. In late July, there were three attempted boardings in less than a week, all off the coast of Sumatra.
In August, a large tanker called the Penrider was attacked while carrying 1,000 tonnes of fuel oil near the Malaysian coast.
Fourteen pirates boarded the vessel, armed with AK-47 and M-16 assault rifles.
The ship's captain was forced to sail into Indonesian waters, where three of the crew were taken hostage. They were only released after protracted ransom negotiations.
Mr Mukundan said there was a lot of evidence which pointed the finger of blame at Gam.
Sailors kidnapped by the pirates in the Penrider incident described their captors as uniformed men who spoke the Acehnese language, he said.
Some of the hostages were even taken to jungle hideouts in Aceh, where the pirates made no secret of the fact that they belonged to Gam, Mr Mukundan said.
Kirsten Schulze, from the Centre for Strategic and International Studies, said it was "definitely possible" for Gam to be behind the attacks.
There are two main reasons why the rebels would see piracy as a possible sideline, she told BBC News Online.
The first is money. Gam rebels are under a lot of pressure at the moment, with more than 40,000 Indonesian troops deployed in Aceh to seek them out.
Without shipments of money and arms, the rebels would be unable to fight the encroaching army.
"If they hold ship crews to ransom, (the rebels) can then raise money to buy weapons," Ms Schulze said.
The second reason for the rebels to turn to piracy is for more ideological reasons.
Many of the recent attacks have targeted oil tankers owned by large multinational firms, which Gam accuse of siding with the Jakarta Government against the wishes of the Acehnese people.
Aceh is a province rich in energy reserves, and one of the rebels' chief complaints is that much of the province's oil wealth ends up in Jakarta.
The rebels "see themselves as defending their natural resources," Kirsten Schulze said.
Gam, however, still maintains it is not involved in piracy.
Gam spokesman Abu Safyan Daud said: "Any international organisation which is pointing its fingers at us - please come and have a look yourself."
Exxon Mobil, one of the companies targeted by the recent attacks, is also reluctant to apportion blame.
More pirate attacks happen near Indonesia than anywhere else
"There was an incident on one of our offshore operations in Aceh in June 2002," said spokeswoman Deva Rachmen. "But we don't know who was behind it."
Even the Indonesians are being noticeably coy.
"It's not been proven yet," said a spokesman for the Indonesian navy.
"There may be one or two people who do piracy for Gam, but not the majority."
As with any reported incident from Aceh, accurate information is difficult to obtain, due to the restricted media access in place since the start of the military crackdown.
But what is clear is that cargo ships and tankers are increasingly at risk on the Malacca Straits - and Gam rebels are increasingly in need of resources to fight the Indonesian military.