Gunmen attacked two cargo vessels off the coast of the oil-producing Niger Delta, killing one crew member and kidnapping several others, a Nigerian navy spokesman said on Saturday.

The crew members seized near Bonny in southern Rivers state on Friday are not yet known, but the military believed they were from eastern Europe.

"Gunmen attacked the cargo vessel BBC Palonia and one other four nautical miles south of Bonny River," said navy spokesman Lt. Edward Yeibo. "The gunmen shot one dead and took others hostage."

No group has claimed responsibility.

Kidnappings for ransom are common in the Niger Delta, home to Africa's biggest oil and gas industries, with hundreds of incidents reported each year. Most victims are released unharmed.

Foreign firms, ranging from oil to construction to telecoms, are forced to spend millions of dollars a year on security for their staff because of the high crime rate in the Niger Delta.

Security officials say former militants fed up with a government amnesty programme could be behind a renewed wave of kidnappings, robberies and oil theft.

President Goodluck Jonathan has made a priority of reviving a post-amnesty programme for thousands of former gunmen who surrendered their arms last year in return for the promise of stipends, education and job opportunities.

The first batch of 2,000 ex-rebels started a four-week rehabilitation class at the amnesty centre in Obubra in Cross River state this week.

But the launch of the programme was marred by violence on Thursday when a small group of former militants angry at the delays attacked a government convoy visiting the amnesty camp.

"We expected these types of challenges, but the programme will continue without delay," said Timi Alaibe, presidential adviser on Niger Delta affairs, who was at the amnesty centre during the incident.

Reuters