Six Russians kidnapped in Nigeria

The Russian ambassador said the attack had taken place in the south-eastern town of Ikot Abasi.

He said he had requested that the Nigerian government take "urgent measures" to secure the men's release.

Kidnappings - more often of oil workers - have become a common occurrence in the south of Nigeria. Victims tend to be released after a ransom is paid.

Two Philippine oil workers were held hostage for a few hours in southern Nigeria on Sunday before being released

The region's main rebel group announced a ceasefire on Saturday.

The Movement for the Emancipation of the Niger Delta (Mend) said it would suspend attacks on oil installations for one month, to allow newly sworn-in President Umaru Yar'Adua "to ruminate on positive and realistic measures towards a just peace in the Delta".

It released six hostages as what it called an olive branch, but did not say it would stop kidnapping.

Apartment blown up

It was not clear which group kidnapped the Russians.

Gunmen entered the residential compound of an aluminium-smelting plant belonging to Russia Aluminium (Rusal), the world's largest aluminium producer.

They blew up their victims' apartment with dynamite before taking them away, Felix Nxong, general manager of the plant, told the Associated Press.

More than 200 foreigners have been kidnapped since militants increased their attacks in late 2005, with more than 100 foreign workers taken this year alone, the Associated Press reported.

More than two dozen foreigners are currently thought to be in captivity.

Eleven were captured in two separate incidents on Friday.

President Yar'Adua has said tackling the unrest in the south is one of his top priorities.