SEOUL - A GROUP of 22 Asian sailors has been released after more than a month of captivity since their cargo ship was hijacked by pirates off the coast of Somalia, a South Korean official said.

Meanwhile, India announced it is is sending naval warships to the troubled Gulf of Aden on an anti-piracy patrol and the Philippines urged foreign ship owners on Thursday to use only safe routes patrolled by the US.

More than two dozen ships have been seized by pirates this year off the Horn of Africa, including an arms-laden Ukrainian ship for which pirates have demanded a US$8 million (S$11.8 million) ransom.

The crew members who were released on Thursday from a South Korean cargo vessel - eight South Koreans and 14 Myanmar citizens - were heading toward a US navy vessel in the area after being set free earlier in the day, Foreign Ministry spokesman Moon Tae Young told reporters.

Mr Moon said the sailors were all safe but declined to comment on whether a ransom was paid.

The South Korean vessel was hijacked by Somali pirates on Sept 10 in the Gulf of Aden. It was also released on Thursday.

The latest incident has prompted the South Korean government to also consider dispatching naval vessels in waters off Somalia to counter any possible hijacking of South Korean ships.

The hijacking of an arms-laden Ukrainian ship freighter carrying a cargo of heavy weapons has heightened concern over the chaos in a key shipping route and prompted Nato to send warships to help US Navy vessels already patrolling the region.

Somalia, which has had no functioning government since 1991, is the world's top piracy hot spot. It is located along the Gulf of Aden, which connects the Red Sea and the Indian Ocean and is one of the world's busiest waterways with some 20,000 ships passing through it each year.

So far, 29 ships have been hijacked this year off the African coast. The latest is a Philippine bulk carrier seized in the Gulf of Aden on Wednesday with a crew of 21, Noel Choong of the Malaysia-based International Maritime Bureau's piracy reporting centre.

The Philippines' Vice-president Noli de Castro appealed to international shipping companies on Thursday 'to take extra precautionary measures' and sail only within the Maritime Security Patrol Area in the Gulf of Aden, which is patrolled by warships and aircraft from a coalition that includes US, British and French forces.

The Philippine Department of Foreign Affairs said pirates seized the bulk carrier African Sanderling and its 21 Filipino crewmen on Wednesday.

The department said the hijacking brought the number of Filipinos being held by pirates to 66 on four ships.

Pirates have seized more than two dozen ships this year off the Horn of Africa, and more than 100 Filipino sailors have been taken in those raids. One died during an attack.

With more than 270,000 Filipinos on thousands of vessels around the world, Filipinos account for about a third of the international shipping industry's crews. -- AP