(Rewrites with MEND statement)

By Tume Ahemba

LAGOS, May 1 (Reuters) - A Nigerian militant group said it abducted six foreign oil workers in an attack on Tuesday on an oil vessel on the Penington River in southern Bayelsa state.

The Movement for the Emancipation of the Niger Delta said the kidnappings were to counter reports that it was in support of Nigeria's president-elect Umaru Yar'Adua and his deputy Goodluck Jonathan, who is also the governor of Bayelsa state.

MEND, which says it is fighting for more local control over the Niger Delta's oil wealth, said the attack should also serve as a warning to Shell over its return to oilfields previously attacked by the group.

MEND identified the hostages taken in the assault on U.S. energy giant Chevron's offshore loading terminal as Italians Raffele Pascariello, Alfonso Frawza, Ignazio Gugliota and Mario Celetano, American John Stapleton, and Croat Juricha Ruic.

"The hostages will be released unconditionally on May 30, 2007," MEND said in an email statement. It added that this would be possible only if oil companies and the government do not try to secure their release by offering ransom.

Security sources said at least one Nigerian was killed in the raid on the vessel, called Oloibiri after Nigeria's first oil well, is operated by Chevron <CVX.N>.

"The militants shot one navy personnel and compelled the crew to throw a rope down to give them access by using dynamite," one security source said.

The attack forced Chevron to shut down 15,000 barrels per day of output at a small offshore oilfield, a company spokesman said in London.

Nigeria's oil output has been reduced by 500,000 barrels per day, or a fifth of production capacity, since a series of raids on Royal Dutch Shell oilfields in February 2006 forced their closure.

SEPARATE ABDUCTION

In a separate incident, unknown gunmen abducted the mother of Rivers state governor-elect Celestine Omeiha from her village near Africa's oil heartland of Port Harcourt, police said.

The abduction is apparently a fall-out from the April 14 state elections -- which monitors said were marred by fraud -- because Niger Delta militants rarely kidnap Nigerians.

In the Niger delta, an increasing number of armed groups demanding jobs, benefits or control of oil revenues have attacked industry facilities, kidnapped expatriate staff and fought with security forces.

But the lines between militancy and crime are blurred in the delta, a vast wetlands in southern Nigeria that accounts for all oil production from the world's eighth biggest exporter but where people are desperately poor and frustrated.

Some groups have taken hostages to press political demands but numerous "freelance" kidnappers have seized foreigners to extract cash from their companies or from government.

Most hostages are released unharmed after a few days although some have been kept in captivity for months and two have been killed in failed attempts by troops to free them.

Thousands of foreign workers and their relatives have fled the Niger Delta since the start of a wave of attacks on oil facilities and kidnappings of foreigners in late 2005. (Additional reporting by Randy Fabi in London, Roberto Landucci in Rome, Austin Ekeinde in Port Harcourt and Tom Ashby in Lagos)

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