Pirates seized a ship with 24 crew members off the port of Aden on Monday and Mogadishu traders said seven additional vessels headed for the
Somali capital had been hijacked over the past two days, Reuters reported.
Kenyan-based Ecoterra maritime monitoring agency said pirates had taken control of a roll-on, roll-off ship called the MV Iceberg 1 on Monday.
"The owners reported to NATO that pirates boarded the ro-ro vessel MV Iceberg 1 today just 10 miles outside Aden Port in the Gulf of Aden," Ecoterra said. "The vessel with her 24 member crew is now commandeered toward the Somali coast."
Andrew Mwangura of the Kenya-based East Africa Seafarers Assistance Programme told Reuters the Panama-flagged ship's crew had citizens of Ghana, Pakistan, India, Sudan and Yemen, and it was seized while en route to the United Arab Emirates.
A spokesman for Mogadishu traders told reporters that another seven boats had been seized as they headed for the Somali capital's seaport. Until now ships bound for Mogadishu have been largely spared by pirates, whose attacks have become bolder and more frequent.
The seven ships cited by the traders did not include a Seychelles fishing vessel and an Iranian boat that were also taken in the waters off east Africa but later freed, according to the Seychelles coast guard.
"Pirates hijacked seven boats in the Indian Ocean in the last 48 hours," the spokesman, Mohamed Omar, said.
"The boats were carrying commercial goods to Mogadishu. Our counterparts overseas do not want their boats hired by Somali traders any more. Piracy is now be very risky to our business."
Sea gangs have acquired millions of dollars in ransoms and defied a flotilla of foreign warships that are trying to monitor the region's busy sea lanes.
They have plagued the busy shipping lanes off Somalia for years. As well as holding some ships for ransom, pirates also hijack vessels to use as 'motherships' which ferry the gunmen and their speedboats far out to sea.
The Seychelles president's office said the fishing vessel, called the Galate, was captured 90 miles off the coast of the archipelago's main island before later being freed. All six crew members were safe.
Seychelles said its coast guard had also rescued 21 crew from the Iranian boat in the same operation.
Separately, the U.S. destroyer McFaul rescued 30 Africans stranded in the Gulf of Aden after their vessel developed engine problems, the U.S. Navy's Fifth Fleet said in a statement.
Last year 50,000 people, many from Somalia, took rickety smugglers' ships across the Gulf of Aden, seeking jobs in the Middle East or fleeing political turmoil at home.
"The 30 men, women and children onboard had been stranded with no food and very little water for nearly four days since departing the Somali coast," the Navy said.