Officials of the Italian oil company Eni SpA said an armed assault on its offices left nine people dead Tuesday in Nigeria's petroleum-rich south, where four foreign oil workers also are being held hostage.

Recent attacks and sabotage in the Niger Delta region have helped drive up international crude prices, although the Italian company said there was no evidence the latest violence was linked to those incidents.

In the latest attack, nine people were killed in a shootout between an armed gang and local security forces at Eni SpA's offices in Port Harcourt, the Italian company said.

The Italian Foreign Ministry said that no Italians were among the victims.

The gunmen exchanged fire with local security forces and briefly occupied a bank near the base, leaving at about 3:30 p.m, about an hour after they showed up, Eni said in a statement.

"Eni has temporarily evacuated staff and contractors from the area of the base affected by the incident and the situation is currently under control," the statement said.

A company official, who spoke on condition of anonymity because the company bars talking to reporters, said the attackers stole cash in what the official characterized as a robbery. Authorities in Port Harcourt could not immediately be reached for comment.

The recent attacks and kidnappings have claimed at least 20 lives, cut Nigeria's daily exports of 2.5 million, and helped send crude prices higher on international markets.

Meanwhile, militants claiming to have taken four foreigners hostage Jan. 11 in the region said the oil workers are in decent health but had been moved deeper into the region of swamps and creeks after the government failed to meet the captors' demands.

Nigeria is Africa's most-populous nation, leading oil producer and the fifth-biggest source of U.S. oil imports.

Despite the massive amount of crude pumped from southern Nigeria, much of the region remains in abject poverty. Activist groups have been agitating for President Olusegun Obasanjo's government to provide them with a greater share of oil revenues.

An e-mail to The Associated Press that claimed be from the Movement for the Emancipation of the Niger Delta said Tuesday that Nigeria had not met the demand to release two of the region's leaders from jail.

"Be assured therefore that the hostages in return, will remain our guests," said the statement, whose authors' identity could not be verified. The kidnappers' demands and news of the conditions of the oil workers, who are from the U.S., Bulgaria, Britain and Honduras, have been sent from the same e-mail address.

The hostages "are in good health and have adapted fairly well to the conditions under which the people of the Niger Delta have been kept," the statement said.

On Saturday, the group's leader told the AP by telephone that the American hostage, Patrick Landry of Texas, was sick and warned that if he dies, his group would kill the remaining hostages.

The militants are demanding the release of Mujahid Dokubo-Asari, a militia leader from the region who is facing treason charges, and Diepreye Alamieyeseigha, a one-time regional governor detained on suspicion corruption.

The militants allege that the two ethnic Ijaw leaders are facing persecution by Obasanjo's government for advocating more local control of oil resources.