MOGADISHU - 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 in the failed Horn of Africa nation have flourished over the past few years.

The gangs 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-flagged bulk 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 way into the Indian Ocean near the Seychelles archipelago.

Somalia's Western-backed government has pledged 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.

ATTACKS ON THE RISE

Analysts say there is scant hope of stamping out the lucrative trade unless some order can be brought to Somalia, an unlikely prospect given that rebel groups control much of the country and the pirates are well-entrenched in their fiefdoms.

According to the International Maritime Bureau there has been a marked rise in pirate attacks worldwide this year from a year earlier. It says 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 and evade the sea gangs.

Andrew Mwangura of the Kenya-based East Africa Seafarers' Association said the chemical tanker and its 26 crew were 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 fertilizer when it was seized. Mwangura said it was believed to have 19 crew members on board, mostly from the Philippines.

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 Horn of Africa nation prior to two latest seizures.

(Reporting by Abdi Guled and Mohamed Ahmed in Mogadishu and David Clarke in Nairobi; Writing by David Clarke; Editing by Alison Williams)

Somalia