Twenty fishermen who were rescued by the Dutch vessel HNLMS De Zeven Provincien off the Somalian coast on Saturday are shown on the Yemeni-flagged dhow that had been seized by Somalian pirates earlier in the week. (NATO/Associated Press)

In the latest high-seas drama off the Horn of Africa, bandits seized a Belgian ship with 10 crewmembers near the Seychelles islands on Saturday and started hauling it toward Somalia, while in a separate incident, NATO forces rescued 20 fishermen from pirates.

In the first attack at pre-dawn, pirates hijacked the Belgian-flagged Pompei a few hundred kilometres north of the Seychelles, a high-end tourist destination.

The ship, carrying a cargo of concrete and stones, sounded three alarms indicating it was under attack, Belgian officials said.

Crew of 10 kidnapped

The ship had 10 crewmembers: two Belgians, one Dutch, three Filipinos and four Croatians.

As pirates steered the vessel toward Somalia, 700 kilometres away, a Spanish military ship, a French frigate and a French scout ship all steamed toward the area to try to intercept it.

Government officials in Brussels held an emergency meeting to discuss possible intervention.

"There is no contact with the pirates, not with the crew, not with any other parties," Jaak Raes, director general of the Belgian Crisis Centre, told reporters.

In a second attack later Saturday, pirates fired at a Marshall Islands-flagged tanker, the Handytankers Magic.

It issued a distress call shortly after dawn but escaped the pirates using "speed and manoeuvres," said Portuguese Lt. Cmdr. Alexandre Santos Fernandes, who is travelling with a NATO fleet patrolling further north in the Gulf of Aden.

NATO forces detain, then release pirates

A Dutch frigate from the NATO force responded immediately to the distress call and trailed the pirates to a Yemeni-flagged fishing dhow the brigands had seized Thursday, Fernandes said.

The bandits were using the Yemeni vessel as a "mother ship," a larger vessel that allows the pirates' tiny motorboats to hitch rides, greatly expanding their range.

The pirates climbed into the dhow, with Dutch marine commandos in hot pursuit. They freed 20 fishermen whose nationalities were not known.

Fernandes said there was no exchange of fire and Dutch forces seized seven automatic weapons and a rocket-propelled grenade launcher.

Seven Somalian pirates were detained, then released because "NATO does not have any detainment policy," Fernandes said.

With files from The Associated Press