More than 130 pirates attacks were reported in 2008
Somali pirates have seized a British-owned cargo ship and a Taiwanese ship, maritime officials say, after capturing three other vessels over the weekend.
The UK-owned Malaspina Castle was boarded in the Gulf of Aden, while the Taiwanese ship was seized near the Seychelles, according to reports.
A French yacht, a Yemeni tugboat and a German ship were also captured in the pirate-plagued waterway at the weekend.
The region is heavily patrolled by a growing international naval coalition.
But correspondents say the pirates have been venturing further off coastal areas to evade the warships from more than a dozen nations patrolling the area in an attempt to deter the gangs.
The 32,000-tonne Malaspina Castle, which was carrying a cargo of iron, was seized on Monday morning.
The vessel, which flies a Panamanian flag, has a crew of 24 - from Bulgaria, Russia, Ukraine and Philippines.
Andrew Mwangura, of the Mombasa-based East African Seafarers' Assistance Programme, told Reuters news agency it is UK-owned but operated by Italians.
The Taiwanese fishing boat, with a crew of 29, was hijacked 260km (160 miles) from the Seychelles.
The French yacht, with four crew, was seized on Saturday off north-east Somalia.
It was being sailed by the pirates towards the Somali Puntland coast, said Kenya-based non-governmental organisation Ecoterra International, which monitors piracy.
The Yemeni tugboat was captured on Sunday, a day after the 20,000-tonne German container vessel, the Hansa Stavanger, was seized.
More than 130 pirates attacks, including close to 50 successful hijackings, were reported in 2008, threatening one of the world's busiest shipping lanes.