FACTBOX-Ships held by Somali pirates

Security forces have deployed to outer islands of the Seychelles archipelago after a second vessel flying the Indian Ocean nation's flag was seized by Somali pirates, the army chief said on Thursday.

At least 15 pirate attacks on vessels off the coast of Somalia were reported by the International Maritime Bureau for March, after just two in January and February.

Earlier hijackings were focused on the Gulf of Aden.

Below are some of the ships believed to be still held by pirates as well as some details on the increase in piracy:

STOLT STRENGTH: Seized Nov. 10. The chemical tanker had 23 Filipino crew aboard. It was carrying 23,818 tonnes of oil products.

CHEMSTAR VENUS: Seized Nov. 15. The tanker was travelling from Dumai, Indonesia, to Ukraine. It had 18 Filipino and five South Korean crew.

NAMES UKNOWN: Seized on Dec. 10. Pirates hijacked two Yemeni fishing vessels with a total of 22 crew in coastal waters in the Gulf of Aden. Five crew reportedly escaped.

NAME UNKNOWN: Seized on Dec. 16. A yacht with two on board, an Indonesian tugboat used by French oil company Total. Pirates also hijacked the Chinese fishing vessel Zhenhua-4 with 30 Chinese crew aboard but it was freed the next day.

LONGCHAMP: Seized on Jan. 29, 2009. The liquefied petroleum gas tanker, built in 1990, has 13 crew on board, 12 Filipinos and one Indonesian. The tanker has a capacity of 3,415 tonnes.

SALDANHA: Seized on Feb. 22, 2009. The Maltese-flagged cargo ship, sailing to Slovenia, has 22 crew and was loaded with coal. TITAN: Seized on March 19, 2009. The 43,000 dwt Saint-Vincent-flagged cargo vessel with 24 crew was sailing from the Black Sea to Korea when it was attacked by pirates.

NIPAYIYA: Seized on March 25, 2009. The Greek-owned and Panamana-registered MT Nipayia, was seized by pirates 450 miles from Somalia's south coast.

BOW ASIR: Seized on March 26, 2009. The 23,000-tonne Bahamas-registered chemical tanker was carrying caustic soda. It was operated by Salhus Shipping and carried 27 crew consists of a Norwegian captain, 19 Filipinos, five Poles, one Russian and one Lithuanian.

INDIAN OCEAN EXPLORER: Seized March 2009: The 35-metre long boat was built in Hamburg as an oceanographic research vessel. It accommodates around 12 passengers. The yacht Serenity with three people on board was seized in late February or early March.

* PIRACY: KEY FACTS:

-- In 2008 there were 293 incidents of piracy against ships worldwide -- more than 11 percent up on the year before. Attacks off Somalia and in the Gulf of Aden increased nearly 200 percent.

-- All types of vessels have been targeted. The pirates boarding the vessels were also better armed than in previous years and prepared to assault and injure the crew.

Sources: Reuters