By Tom Ashby

LAGOS, June 2 (Reuters) - Gunmen disguised as riot police abducted four foreign workers from the residential compound of oil services giant Schlumberger <SLB.N> in Nigeria's oil city Port Harcourt, authorities said on Saturday.

In nearby Bayelsa state, a group at the vanguard of delta militancy freed six foreigners -- four Italians, one American and a Croatian -- it seized on May 1 from a facility operated by U.S. oil giant Chevron <CVX.N>.

The Movement for the Emancipation of the Niger Delta (MEND) also said it would halt attacks for one month to pave the way for talks with the new Nigerian government.

Kidnapping has become an almost daily occurrence in the anarchic Niger Delta, home to Africa's largest oil industry, and about 24 foreigners are still being held by various armed groups in the vast wetlands region.

"Some expats were kidnapped from the club of Schlumberger Anadrill in a residential area last night," said Rivers state police commissioner Felix Ogbaudu. The abductors were dressed as riot police, he said.

Schlumberger Anadrill is a private subsidiary of U.S.-listed Schlumberger, the world's largest oil services company.

The company said the four hostages were citizens of Britain, France, the Netherlands and Pakistan. "We are working with the relevant agencies to resolve the situation as quickly as possible," Schlumberger said in a statement.

Attacks on oil facilities and kidnappings have forced thousands of foreign workers to flee and reduced oil output from the world's eighth-largest exporter by almost a million barrels a day, one third of Nigeria's capacity.

Some armed groups say they are fighting for more autonomy for the impoverished oil province of southern Nigeria, but the line between militancy and crime is blurred and most abductions are by groups seeking ransom.

Gunmen used dynamite and machineguns to seize at least three top Indian managers of Indonesian chemical company Indorama from their residence near Port Harcourt on Friday. Diplomatic sources said the gunmen also took three family members.

CEASEFIRE

The British government last week advised its citizens to avoid all travel to the Niger Delta. "The situation is getting worse," one Western diplomat said.

The crisis in the delta is a major priority for the new government of President Umaru Yar'Adua, who took office on Tuesday and used his inaugural address to appeal for an end to the violence.

Yar'Adua had announced a summit on the region starting on Monday but the presidency postponed it on Saturday because participants had asked for more time to consult.

MEND advised Yar'Adua not to follow the example of his predecessor, Olusegun Obasanjo, who staged similar summits and had little to show for them.

The rebel group said it would talk to the government only through intermediaries it had appointed, in the presence of a neutral arbiter acceptable to all parties.

MEND has demanded regional control over the delta's oil wealth, the release of two jailed leaders from the region and compensation to delta villages for oil pollution.

The group said it "will resume attacks on installations and oil workers in the delta with greater purpose" after the one-month grace period. (Additional reporting by Tume Ahemba)

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