About a dozen gunmen attacked a Total SA oil pumping station in Nigeria early Thursday, killing three police guards and shutting down the facility, company officials said.

Meanwhile, oil firm Royal Dutch Shell PLC began evacuating all family members of foreign workers as a precaution against a worsening security situation in the oil-rich delta.

About 12 men attacked a residential compound "a relatively large distance" from the oil production site, which was not attacked, Total spokesman Paul Floren said by phone from Paris.

A Total official in Nigeria's capital, Abuja, said the pumping station in the Obagi oil field had been shut down. The Nigerian official spoke anonymously because the information had not yet been cleared for public release.

Floren said the station usually produces about 40,000 barrels a day. He did not say whether it had been shut down.

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Nigeria, Africa's biggest oil producer and the fifth-largest U.S. supplier, has seen its typical oil production of 2.5 million barrels per day cut by a quarter this year by a series of attacks and hostage-takings by militants — some seeking ransoms and others political influence.

Gangs and politically minded militants say attacking the oil infrastructure is their only way to get a share of the country's oil wealth.

Floren said Thursday's attack was not political.

"They were looking to steal," he said, saying the assailants broke into offices, but it was unclear if they took anything.

They have since left and the site is secure, Floren said, adding that no hostages were taken.

Floren said Total operates the pumping station, and owns a 40 percent share of the facility.

He added that Total regretted the deaths of the police officers.

Four Total employees were slightly injured and were taken to a hospital, Floren said. He said he had no information on whether any attackers were killed or injured.

On Monday, militants detonated two car bombs at oil company compounds in the southern river delta region that produces most of Nigeria's crude.

One of the major groups, the Movement for the Emancipation of the Niger Delta, or MEND, claimed responsibility for the attack, saying that it was part of an ongoing effort to free a group of militant leaders imprisoned by the government. There were no injuries reported.

Royal Dutch Shell PLC began evacuating all dependents of foreign employees from the delta region Thursday, citing the deteriorating security situation following the car bombs — one of which was set off in a Shell complex.

The move was "a precautionary measure," company spokesman Bisi Ojediran said. He declined to say how many people were being evacuated, but many in Nigeria's oil industry said hundreds were likely to be affected.

Ojediran said he could not recall the last time Shell took such a move, saying it was "the first time in recent times" that the company decided to evacuate all family members.

Total's Floren did not say if the company was considering any similar measures.

"We have put all measures in place to ensure that our employees are secure in Nigeria," he said. He said he could not discuss the measures for reasons of security.

MEND has also been holding four foreign oil workers hostage since early this month, having captured them in an attack on an oil export station belonging to Agip, a subsidiary of Italian oil firm Eni SpA.

The group, which has e-mailed pictures of the hostages, has said they will not be released until Nigerian authorities free Mujahid Dokubo-Asari, a militant leader on trial on treason charges, and Diepreye Alamieyeseigha, former governor of a southern state, on trial on money-laundering charges.