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By Randy Fabi

ABUJA, Oct 4 (Reuters) - Gunmen in Nigeria kidnapped six Filipino workers during an attack on an oil service vessel in the Niger Delta, security sources said on Saturday. A speedboat carrying 12 gunmen attacked the vessel and took six hostages, including the boat's captain and two engineers, two sources said. No group has claimed responsibility for the attack.

"The vessel was attacked in between Port Harcourt and Bonny," said a private security source, who asked not to be named.

More than 200 foreigners have been kidnapped in the Niger Delta, the heart of Nigeria's oil sector, since early 2006. Almost all have been released unharmed.

In a separate incident, gunmen on Saturday released a Briton kidnapped more than two weeks ago in southern Nigeria.

"We can confirm a British national, kidnapped on Sept. 15 in Port Harcourt, Nigeria, was released on Oct. 4. He has been visited by consular staff and is safe and well," a British Foreign Office spokesperson said.

Lieutenant Colonel Sagir Musa, spokesman for the military task force in Rivers state, said no ransom was paid for the release of the Briton, a former employee of the petrochemicals firm Indo Rama.

Insecurity in Nigeria, the world's eighth largest oil exporter, has cut crude output by around a fifth since militants launched their campaign of violence two years ago to press for greater development in their neglected communities.

Criminal gangs in the delta, a vast network of mangroves opening into the Gulf of Guinea, have taken advantage of the breakdown in law and order. Kidnapping for ransom of businessmen, local politicians and foreign workers are common. (Additional reporting by Austin Ekeinde in Port Harcourt and Matt Falloon in London)

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