A helicopter fired warning shots toward a suspected pirate skiff, where six Somali men sat among assault rifles, grappling hooks and an aluminum ladder. But before it could be boarded by sailors from a nearby warship, the men threw all the gear overboard.

With little evidence to convict them, the would-be pirates were let go, along with their boat and enough fuel to get to Somalia. Nothing was done to prevent the men from rearming and trying again.

The high-seas encounter last week illustrates how the multinational naval force deployed a year ago to try to stem piracy has had limited success. Experts say the attacks won't stop unless pirate havens inside Somalia are eliminated.

But that goal remains elusive. The U.N.-backed Somali government can barely hold a section of the capital, let alone go after onshore pirate havens. Foreign governments are reluctant to deploy ground forces.

Pirate attacks nearly doubled in 2009 over a year earlier, despite the deployment in December 2008 of the European Union Naval Force _ the first international force specifically to counter Somali pirates.

Somali pirates currently hold at least 10 vessels and more than 200 crew members for ransom.

Still, proponents of the force note the pirates' success rate has been cut roughly in half since the patrols began.

"A lot more ships would have been taken if we weren't there," Cmdr. John Harbour, the force's spokesman, told The Associated Press. He said the pirates had not seized any ships in the heavily trafficked Gulf of Aden since July, which he called evidence of the force's impact.

Somali pirates tried to board at least 209 vessels this year through mid-December, seizing 43 of them, the International Maritime Bureau says. That compares to 42 successful attacks out of 111 attempts in 2008, before the EU Naval Force deployed.

The pirates have responded to the presence of the sleek gray warships from NATO, the European Union, Japan, South Korea and China by turning their attention to less protected waters.

To carry out raids beyond the heavily patrolled maritime corridors, pirates have begun using captured vessels as motherships, enabling them to attack vessels as far as 1,000 miles off Somalia's coast, Harbour said.

"We can't say that anyone has won the war against piracy, it's still very much ongoing," said Cyrus Mody at the International Maritime Bureau. "There is still a significant amount of piracy. It has not reduced since last year."