Somali pirates have hijacked a Comorian-flagged vessel with 29 crew on board in the Somali basin, European Union anti-piracy force said on Thursday.

EU Naval Force Somalia spokesman Per Klingvall said the MV Aly Zoulfecar was seized on Wednesday in waters between the Comoros and Dar Es Salam, Tanzania.

The MV Aly Zoulfecar has 29 people onboard, of which 9 are crew members and 20 are passengers. The crew consists of one Tanzanian, four Comorians and four from Madagascar.

"The passengers consist of 12 Tanzanians and eight Comorians. This makes a total of 13 Tanzanians, 12 Comorians and 4 Malagasy on board the pirated vessel," Klingvall said.

He said the 43 meters long vessel was in transit from the Comoros to Dar es Salam when it was attacked.

Pirates are holding more than 20 ships with a total of nearly 400 hostages, according to the European Union Naval Force Somalia.

Most hijackings end without casualties after a ransom is paid, but often after several months of negotiations.

The Gulf of Aden, a body of water between Somalia and Yemen, is the main sea route between Europe and Asia.

Tankers carrying Middle East oil through the Suez Canal must pass first through the Gulf of Aden. About 4 percent of the world's daily oil supply is shipped through the gulf.

The attacks are being carried out by increasingly well-coordinated Somali gangs armed with automatic weapons and rocket-propelled grenades, maritime officials said.

The Horn of Africa nation has been without a functioning government since 1991, and remains one of the world's most violent and lawless countries.

Combined Task Force 150, a naval alliance dominated by the United States and based in the Gulf of Aden nation of Djibouti, is patrolling an area within the Gulf of Aden to help protect ships from pirates.