A Portuguese warship seized explosives from suspected Somali pirates after thwarting an attack on a Norwegian-owned oil tanker in the Gulf of Aden, a NATO spokesman said Saturday.

It was the first time NATO forces found pirates armed with raw explosives, Lt-Cmdr. Alexandre Santos Fernandes said from the Portuguese frigate the Corte-Real.

The four sticks of P4A dynamite — which could be used in demolition, blasting through walls or potentially breaching a the hull of a ship — were destroyed along with four automatic rifles and nine rocket-propelled grenades also confiscated. It was unclear how exactly the pirates planned to use the dynamite, Fernandes said.

The Corte-Real had sent a helicopter to investigate a distress call from the crude oil tanker MV Kition late Friday about 100 miles north from the Somali coast.

The suspects fled to a larger pirate vessel, but were intercepted by the warship an hour later.

"The skiff had returned to the mothership," Fernandes said, referring to the vessels pirates commonly use to tow their small, fast speed boats hundreds of miles out to sea. "Portuguese special forces performed the boarding with no exchange of fire." The Bahamian-flagged tanker also was unscathed, he said.

The 19 pirate suspects were released, however, after consultation with Portuguese authorities because they had not attacked Portuguese property or citizens. Decisions on detaining piracy suspects fall under national law; Fernandes said Portugal was working on updating its laws to allow for pirate suspects to be detained in such situations.

Nearly 100 ships have been attacked this year by pirates operating from the lawless Somali coastline despite the deployment of warships from over a dozen countries to protect the vital Gulf of Aden shipping route.