ABUJA - Nigeria's military said on Friday it had inflicted heavy losses on Islamist militant groups in the north and oil thieves in the south, arresting hundreds, seizing weapons and rescuing kidnap victims in a week-long operation.

Defence spokesperson Major-General Edward Buba said in a statement that troops had killed or wounded 188 militants and arrested 330 suspects across different locations in the country.

Security forces also arrested 36 suspected oil thieves in the Niger delta region and freed 133 kidnap victims, seizing around 270 weapons and more than 5,000 rounds of ammunition during the entire operation.

"The armed forces are working decisively to kill the terrorists, stop insecurity and ensure the safety of citizens. Troops will continue to operate with tremendous forces against the terrorists across the country," Buba said.

Nigeria faces a raft of security challenges including a long-running Islamist insurgency in the northeast, separatist violence in the southeast, rampant oil theft in the Niger Delta and kidnapping for ransom by criminal gangs.

Buba said troops destroyed 51 dugout pits, 24 boats, 21 storage tanks and more than 20 illegal oil refining facilities, recovering nearly 700,000 litres of stolen crude oil.

Oil theft and illegal refining is rife in Nigeria's oil-rich delta as impoverished locals and more sophisticated criminal gangs pilfer pipelines to make fuel to sell for profit.

About 637.7 million naira ($554,500) of suspected proceeds of oil theft was also seized, Buba said. REUTERS