Five Indian sailors kidnapped off Nigeria's oil-rich southern delta and held captive for more than a month have been released by their abductors, a spokesman said Saturday.

The sailors had been seized Dec. 17 as their ship, the SP Brussels, sat 64 kilometers off the coast of the Niger Delta.

The men were in good health after their release and received medical checkups before being flown back to India, said a statement released Saturday on behalf of the ship's operator, Medallion Marine.

"Medallion Marine wishes to express their admiration for the crew and their families who have shown great courage and fortitude throughout this very difficult situation," the statement read.

Martin Baxendale, a spokesman for Medallion Marine, declined to comment Saturday on the exact circumstances of the sailors' release. Typically, most foreign hostages are held for days or weeks until a ransom amount is negotiated. Foreigners can attract ransoms into the hundreds of thousands of dollars.

Foreign oil companies have pumped oil out of the Niger Delta, a region of mangroves and swamps the size of Portugal, for more than 50 years. Despite the billions of dollars flowing into Nigeria's government, many in the delta remain desperately poor, living in polluted waters without access to proper medical care, education or work. The poor conditions sparked an uprising in 2006 by militants and opportunistic criminals who blew up oil pipelines and kidnapped foreign workers.

That violence ebbed in 2009 with a government-sponsored amnesty program that offered ex-fighters monthly payments and job training. However, few in the delta have seen the promised benefits and sporadic kidnappings and attacks continue. The end of the year in Nigeria usually sees an increase in criminal activity, as criminal gangs target the wealthy returning to the country to celebrate the holidays.