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By Austin Ekeinde

PORT HARCOURT, Nigeria, March 17 (Reuters) - Nigerian security forces raided a rundown district near the Niger Delta oil city Port Harcourt on Saturday looking for ransom-seeking kidnappers and other criminals, the military and witnesses said.

A 100-strong team of soldiers, police and secret police ransacked scores of houses in the village of Ogbakiri in the Emuoha local government area of Rivers state and burned the property of suspected criminals.

Thousands of foreign oil workers have fled the Niger Delta, the heartland of Africa's oil industry, since last year because of an increase in militant raids on installations, robberies and kidnappings in the lawless region.

"We were informed that most of the kidnappings and armed robberies were masterminded by these criminal gangs," said Major Sagir Musa, a spokesman for the military Joint Task Force (JTF) that carried out the raid.

He said the raids would continue until the gangs were flushed out completely.

At least one house was burned down and a number of suspects were arrested during the operation in Ogbakiri, a known criminal hideout, witnesses said.

"They moved from house to house, broke through doors, brought out the property of suspects, like electronics, and burnt them," one witness said, asking not to be named for security reasons.

On Friday, the JTF arrested a suspected militant and a group of civilians, recovering a small number of arms, in another raid on the neighbouring Isiodu community.

A few days earlier, on Monday, the JTF rescued two Croats and a Montenegrin who were held for three weeks by suspected ransom-seekers in Ogbakiri, a village outside of Port Harcourt.

Oil workers, they were taken on Feb. 18 from a bar outside their base in Port Harcourt, the capital of Rivers state. Their rescue came hours before armed robbers attacked a passenger boat at the nearby Bonny Island, killing two policemen.

Robberies and the kidnapping of expatriate oil workers, mostly for ransom, increased in January and February in the Niger Delta, which accounts for all of the oil output of the world's eighth biggest crude exporter.

The last of dozens of foreigners in the last four months -- a French oil worker taken hostage by suspected ransom seekers -- was rescued by troops on Friday after five weeks in captivity.

Two Italians were released on Thursday after being held for 98 days by the Movement for the Emancipation of the Niger Delta, a militant group that staged a wave of violent attacks on oil installations last year, cutting off a fifth of Nigerian output.

The group, which emerged in late 2005, says it is fighting for greater autonomy for Africa's top oil region.

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