PORT HARCOURT, Nigeria (Reuters) - Gunmen attacked two cargo vessels off the coast of the oil-producing Niger Delta, killing one crew member and kidnapping 12 foreign workers, Nigerian navy officials said on Saturday.

The crew members seized near Bonny in southern Rivers state on Friday have not been identified, but the military believe they are from eastern Europe.

A security official said the hostages were from Germany, Latvia, Lithuania, Russia and Ukraine.

“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.”

Military officials were in contact with the kidnappers, demanding the immediate release of the hostages, said a navy commander in the capital Abuja.

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 program could be behind a renewed wave of kidnappings, robberies and oil theft.

President Goodluck Jonathan has made a priority of reviving a post-amnesty program 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 center in Obubra in Cross River state this week.

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

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