LAGOS, Nigeria (AP) -- A police spokesman in Nigeria's oil-rich southern delta says gunmen have ambushed officers there, leaving 12 "missing."

Bayelsa state police spokesman Alex Akhigbe said the attack happened Friday near Azuzama, where the officers were on an unspecified special assignment. Akhigbe said the officers' boat broke down and the militants ambushed them in the state's winding creeks.

This is the first major attack in the region in after months of an uneasy calm. Akhigbe declined to say whether authorities believed the officers had died.

Militants and criminal gangs launched an intense campaign of pipeline bombings and foreign worker kidnappings in 2006. By 2009, however, many gave up their weapons as part of a government-sponsored amnesty program. However, sporadic violence has continued, as has major crude oil thefts from pipelines.