Somali pirates have seized a 20,000-tonne German container vessel in their latest attack on the Indian Ocean's busy commercial shipping lanes, a regional maritime group said.

Heavily armed gangs from the lawless Horn of Africa nation hijacked dozens of vessels there and in the strategic Gulf of Aden last year, taking hundreds of sailors hostage and taking  million of dollars in ransoms.

Foreign navies rushed warships to the area in response, reducing the number of successful attacks in recent months. But there are still near-daily attempts.

Andrew Mwangura of the Mombasa-based East African Seafarers' Assistance Programme said the latest hijacking happened on Saturday about 400 miles off the southern Somali port of Kismayu, between the Seychelles and Kenya.

"We believe the German ship has 24 crew on board. We're trying to establish their identities and the name of the vessel," Mwangura told Reuters.

Somali pirates seized two European-owned tankers late last month. Last week the Seychelles military deployed security forces on its outer islands after the pirates hijacked a second vessel flying the Indian Ocean nation's flag.

The pirates typically use speed boats launched from "mother ships". They then take captured vessels to remote coastal village bases in Somalia, where they have usually treated their hostages well in anticipation of a sizeable ransom payment.

In January, Somali gunmen freed the Sirius Star -- a Saudi supertanker loaded with $100 million worth of crude oil -- and its 25 crew after $3 million was parachuted onto its deck.

Last September, they also grabbed world headlines by seizing a Ukrainian cargo ship carrying 33 Soviet-era T-72 tanks. It was released in February, reportedly for a $3.2 million ransom.

The pirates say the arrival of high-tech foreign warships in the waters off their country has made their work more dangerous. One gang member, who asked not to be named, told Reuters in the northern port of Bosasso that he had been part of an aborted attack on another large commercial vessel late on Saturday.

 "We opened fire on a ship near the Gulf of Aden, but our ladder was too short to climb up," he said. "It escaped at high speed. We were nine pirates in two speed boats and immediately we came back. We feared attacks by the warships."  - Reuters