Somali pirates seized a chemical tanker and a cargo vessel on Monday, underlining the continued risk to shipping in some of the world's busiest maritime trade routes.
Somalia has been mired in chaos with no effective central government since 1991 and pirate gangs operating from coastal havens have flourished over the past few years.
They have made tens of millions of dollars from seizing ships for ransom in the Gulf of Aden, linking Europe to Asia, and are also hunting far into the Indian Ocean to evade foreign navies sent to protect commercial shipping.
On Monday, pirates seized the British-flagged chemical tanker St James Park in the Gulf of Aden and the Panama-registered cargo ship Navios Apollon, taking the number of vessels they hold to more than 10, maritime officials said.
On the same day, pirates released the Singaporean-flagged container ship Kota Wajar, saying they received a $4 million ransom for the vessel seized in October far out in the Indian Ocean near the Seychelles archipelago.
An official with Navios ShipManagement, the managers of Navios Apollon, said the vessel was seized about 800 miles off the Somali coast, north of the Seychelles. The official, who declined to be named, said there had been no contact since.
Somalia's Western-backed government has promised to battle piracy but it controls little more than a few blocks of the capital Mogadishu, and the hefty ransoms are attracting more investors in piracy from within the country and abroad.
Analysts say there is scant hope of stamping out piracy unless some order can be brought to Somalia, an unlikely prospect as rebel groups control much of the country and the pirates are well entrenched in their fiefdoms.
Foreign navies have been deployed around the Gulf of Aden and have operated convoys as well as setting up and monitoring a transit corridor for ships to pass through vulnerable points.
The European Union force, numbering seven vessels currently, is among navies with warships in the Gulf of Aden. But forces have been stretched over the vast expanses of water including the Indian Ocean, leaving vessels vulnerable.
According to the International Maritime Bureau pirate attacks worldwide have risen sharply this year. The increased activity and range of Somali pirates has been behind the increase.
In the year to October 20, there were 324 attacks worldwide with Somali pirates accounting for 174 - up from 194 incidents in the same period of 2008. Of the 37 vessels seized, Somali pirates accounted for 35 and took 587 crew hostage.
The raids carried out by heavily armed men in high-speed skiffs have pushed up shipping insurance premiums and forced some vessels to switch routes to try to evade the sea gangs.
Andrew Mwangura of the Kenya-based East Africa Seafarers' Association said the chemical tanker and its 26 crew had been sailing to Thailand from Spain with a chemical used to make plastics when it sent a distress signal from the Gulf of Aden.
He said crew members were from Bulgaria, Georgia, India, the Philippines, Poland, Romania, Russia, Turkey and Ukraine.
The Panama-flagged bulk vessel was sailing from the United States to India with a cargo of fertiliser when it was seized. The Greek management company confirmed there were 19 crew.
According to Ecoterra International, a group that monitors shipping off Somalia, at least 10 foreign vessels and 228 seafarers were being held close to the country before the two latest seizures.