Gunmen in southern Nigeria have taken six Russians hostage, in the latest kidnapping to hit the volatile Niger Delta region.

The six men were working at ALSCON, an aluminum company controlled by the Russian aluminum giant RUSAL.

Russia's ambassador to Nigeria, Igor Melikhov, says bandits seized the men after storming ALSCON's residential quarters Sunday, in the town of Ikot Abasi. He says a Nigerian driver was killed during the raid.

Russian officials are demanding that Nigerian authorities take "urgent measures" to free the kidnapped Russians.

It was not clear who was responsible for the abductions. But kidnappings of foreign workers happen frequently in the Niger Delta. Some are the work of criminal gangs seeking ransom, while others are carried out by militants demanding that local villages get more of the region's oil wealth.

On Saturday, a prominent Nigerian militant group promised to stop attacking oil facilities for one month.

The Movement for the Emancipation of the Niger Delta did not offer to stop kidnapping workers, but released six hostages it had been holding for several weeks.

The group called its moratorium an "olive branch" toward Nigeria's new president, Umaru Yar'Adua.

Nigeria is Africa's largest oil producer but output has been down about 25 percent since last February because of the kidnappings and attacks on oil facilities.

Some information for this report was provided by AFP and Reuters.