MOMBASA, Kenya — Suspected Somali pirates have hijacked a Kenyan-flagged fishing boat with 16 crew which may be used as a "mother ship" to launch more attacks in the Indian Ocean, maritime sources said Tuesday.

Andrew Mwangura, the head of the East African Seafarers Assistance Programme said that the MV Sakoba had a Spanish captain and 15 other crew members from Kenya, Poland, Senegal, Cape Verde and Namibia.

"The vessel was taken hostage in waters off the Kenyan and Seychellois coasts last week", he said.

The European Union's Atalanta anti-piracy naval mission confirmed in a statement that the ship was in the hands of pirates Tuesday and heading towards the Somali pirate lair of Harardhere.

"The Kenyan flagged fishing vessel Sakoba is reported hijacked 400 nautical miles east of Dar es Salam," the statement said.

Atalanta spokesman John Harbour told AFP that the ship's ownership was unclear and voiced fears that the hijacked vessel might be used by the pirates as a floating base from which to launch their skiffs on more victims.

"We dont know who owns the ship. We know that in 2007 it was Spanish owned," Harbour said. "In fact, that ship might have been used by pirates as a mother ship."

Spain's fisheries federation Cepesca said in a statement that the ship's operator was Kenyan while the foreign ministry stressed that "the only connection with Spain is that the captain is Spanish."

Mwangura said the case was suspect since no attempt has apparently been made by the pirates to contact the owners or operators and start negotiations for a ransom payment.

"Communication with the ship has not been established", he said. "It is very strange because in all other pirate attacks, the hijackers make contact with the ship's owners for the sole purpose of negotiating for a ransom."

The UK Maritime Trade Organisation urged seafarers to avoid sailing too close to the Somali coast.

"The fishing vessel is used as a pirate platform and still poses a threat to mariners," it said.

Ecoterra International, a environmental NGO monitoring maritime activity in the region, said the MV Sakoba had a murky track record.

In 2005, the MV Sakoba, then comprising a crew from Kenya and Spain and registered in Ghana, was involved in an incident during which the Kenyan crew members were injured.

Somali pirates, who raked in at least 60 million dollars in ransom money last year, currently hold at least seven ships and close to 150 seamen hostage.

Over the past year, Atalanta and several other multinational naval missions have curbed piracy in the Gulf of Aden -- one of the world's busiest maritime trade routes -- but sea bandits have since ventured further south into less heavily-patrolled areas of the Indian Ocean.

Hundreds of young Somalis have been arrested in the past few days in the Ethiopian capital Addis Ababa.

A number were questioned and then released but it is thought at least 200 are still being held.

Most of the arrests took place on Tuesday night and Wednesday in the Bole area, the part of the town where most of the Somali community live.

A Somali embassy spokesman said he understood that security was being tightened before a regional summit.

In some cases young men were taken from their homes while others were arrested in the streets.

A spokesman for the Somali embassy in Addis Ababa said he and his colleagues were going around the police stations to find out what was going on.

No explanation

He said that following the initial round-up, police were now working their way through those arrested, checking their papers, fingerprinting them and then, if everything was in order, letting them go.

He said that as of Friday morning he believed that around 200 Somali citizens were still being held.

Asked how the embassy felt about the raids, the spokesman said he could not say they were happy but that this was the prerogative of the Ethiopian government.

He understood it had security concerns in the Bole area which is close to Addis Ababa's international airport, especially in the light of the upcoming African Union summit, and he added that if there was a security threat in Bole, then the embassy itself could be the first target.

Somalia's President Abdullahi Yusuf has told parliament he has resigned - a move which adds to the chaos in the country as Ethiopian troops withdraw.

Mr Yusuf's resignation follows a power struggle with Prime Minister Nur Hassan Hussein, who parliament backed after Mr Yusuf tried to sack him.

Ethiopian soldiers, who support the government, are due to pull out this week, raising fears of a power vacuum.

Various Islamist and nationalist groups control most of southern Somalia.