Special forces on a Portuguese warship seized explosives from suspected Somali pirates after thwarting an attack on an oil tanker, but later freed the 19 men. Hours later and hundreds of miles away, another band of pirates hijacked a cargo ship, a NATO spokesman said Saturday.

Pirates are now holding 17 ships and around 300 crew, including the British-owned cargo ship Ariana, hijacked overnight with its Ukrainian crew.

The attack on the Ariana, about 1,000 miles (1600 kilometers) from the sea corridor NATO guards and the seizure of explosives from the group that attacked the crude oil tanker MV Kition may indicate the pirates are adapting their tactics as crews become better trained in counter-piracy measures.

Sailors are aware that pirates generally attack during the day and that some guidelines suggest designating a safe room with a bulletproof door where crews can lock themselves in case of an attack. Such a room would still be vulnerable to being blown open with explosives.

It was the first time NATO forces found pirates armed with raw explosives, Lt. Cmdr. Fernandes said from the Portuguese frigate the Corte-Real, which responded to the attack. The Corte-Real had sent a helicopter to investigate a distress call from the Greek-owned and Bahamian-flagged Kition late Friday about 100 miles (161 kilometers) north from the Somali coast in the Gulf of Aden.

The suspects fled to a larger pirate vessel without damaging the Kition, 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 (kilometers) out to sea. "Portuguese special forces performed the boarding with no exchange of fire."

They found four sticks of P4A dynamite — which can be used in demolition, blasting through walls or potentially breaching a the hull of a ship — which were destroyed along with four automatic rifles and nine rocket-propelled grenades. It was unclear how the pirates planned to use the dynamite, Fernandes said, because there were no translators to conduct interrogations.

The 19 pirate suspects were released after consultation with Portuguese authorities because they had not attacked Portuguese property or citizens. NATO said earlier that the Ariana was Norwegian-owned, but the ship's operators, Oslo-based Polyar Tankers AS, said it was owned by Greek ship-owner Polys Haji-Ioannou.

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 deployment of warships from over a dozen countries to protect the vital Gulf of Aden shipping route.

The latest seizure was the Maltese-flagged Ariana, said Lt. Cmdr. Fernandes, seized overnight northwest of the Seychelles islands. He said the crew members are all Ukrainian but ship-owner Seven Seas Maritime Ltd. has not given the exact number of people onboard.

One hijacked vessel, the Philippine tanker MT Stolt Strength, was held more than five months before a $2.5 million ransom was paid and the ship and 23 crew were released April 21.

Anxious relatives greeted the freed crew in a tearful homecoming Saturday at Manila airport.

The Somali pirates had seized the chemical tanker in the Gulf of Aden on Nov. 10 while it was on its way to India with a cargo of phosphoric acid.

After dropping the pirates close to shore, the ship remained vulnerable, unable to speed to a safe harbor because it was low on fuel. German, U.S. and Chinese naval vessels eventually came to their aid, providing food, medicine and fuel, which allowed them to sail to Oman where they stayed for two days before flying home to Manila.

Second Mate Carlo Deseo said the pirates' evident disorganization was the source of much of his fear.

They "did not seem to know what they were doing," he said.