Dutch commandos have freed 20 fishermen whose vessel was hijacked by Somali pirates and used to launch an attack against a tanker in the Gulf of Aden.
The captives, all Yemeni, were freed when Dutch forces chased pirates back to the fishing dhow.
It was being used by the pirates as a "mother ship" from which to launch armed attacks on commercial shipping.
Meanwhile, Belgian officials say pirates have captured a dredger, the latest in a surge of pirate attacks.
The vessel, the Pompei, had been en route to the Seychelles.
The Dutch took action after receiving a distress call from the Greek-managed tanker.
We have freed the hostages, we have freed the dhow and we have seized the weapons
Intercepting the pirates, the troops then boarded the fishing vessel and freed the 20 Yemenis.
They had been held hostage since Sunday, Nato spokesman Alexandre Santos Fernandes said.
"We have freed the hostages, we have freed the dhow and we have seized the weapons," he told the Reuters news agency.
The spokesman said the pirates were set free because Nato does not have a maritime detainment policy, meaning Dutch national law would apply in this case.
"They can only arrest them if the pirates are from the Netherlands, the victims are from the Netherlands, or if they are in Netherlands waters," he said.
Meanwhile, Belgium's government has told the BBC that a Belgian-registered ship has been captured by Somali pirates.
There had been no communication with the dredging vessel, the Pompei, since it sent two alarm signals early on Saturday.
We tried to have a contact with the ship but without success until now. We suspect it was hijacked by Somali pirates
Belgium government spokesman
The ship, with 10 crew including two Belgians, was about 600 km (373 miles) from the Somali coast and heading for the Seychelles. Satellite pictures show that the ship is not moving.
"This morning we received through two different channels, a silent alert, that there was a problem on the boat, which is a Belgian boat on its way to the Seychelles," said Peter Mertens, a spokesman for the Belgian government's crisis centre.
"We tried to have a contact with the ship but without success until now.
Reuters quoted an unnamed pirate as confirming the hijack in a telephone call in which he said the attackers would take the ship to the Somali port of Haradheere.
Pirates have intensified attacks on shipping in recent weeks in one of the world's busiest sea lanes, despite patrols by the US and other navies.
Reports say they are currently holding more than 280 crew members and 15 cargo ships.
The Dutch success is the latest in a string of recent Western military operations against the pirates.
French and US troops have both taken action against pirates in recent days. The French rescued three people from a captured yacht in an assault which saw one man killed.
Earlier this week US troops killed three pirates and captured another as they rescued the American captain of a tanker from captivity.
US Secretary of State Hillary Clinton recently unveiled a plan to tackle piracy in the Gulf of Aden and the Indian Ocean off Somalia.
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