Nigeria ? Nigeria’s volatile Niger Delta is unlikely to see a reduction in violence, despite Monday’s release of four kidnapped foreign oil contractors, analysts say.

The oil-rich region is notorious for its violence, political corruption, large-scale oil theft and kidnappings.

Militants released the four after holding them nearly three weeks, but immediately threatened new attacks and warned foreign oil workers to leave.

Nigeria is the fifth-largest supplier of U.S. oil.

The four, Patrick Landry, of America, Nigel Watson-Clark, of Britain, Milko Nichev, of Bulgaria, and Harry Ebanks, of Honduras, were kidnapped on Jan. 11.

The Movement for the Emancipation of the Niger Delta claimed responsibility.