Army spokesman Lieutenant-Colonel Musa Sagir said half of those picked up were still being held by the police or have appeared before the courts, while the rest were freed due to lack of incriminating evidence, he said.
"From conservative estimates, around 300 suspects have been arrested," Sagir, spokesman of a special task force comprising the military and police deployed to the region in southern Nigeria, told AFP.
"As a result of the past weeks' crisis, the militants admitted that they had lost some men, and it was because of the losses they encountered that they went into the communities to try and beef up their numbers," he added.
On Sunday last week, exactly seven days after it launched a week-long offensive in which it claimed six attacks on facilities run by multi-national oil firms, the Movement for the Emancipation of the Niger Delta (MEND) said it was calling a unilateral ceasefire until further notice.
MEND had declared "war" on the oil industry in what it said was a response to an attack by the Nigerian army on its positions, and vowed to reduce Nigeria's oil exports to "zero".
The group contends that the oil wealth of Nigeria - now Africa's second largest petroleum exporter after recently falling behind Angola -- does not sufficiently benefit the local population.
It also accuses oil companies of wreaking havoc on the environment.
MEND has not commented on the spate recent arrests of suspected militants.
Militant attacks in the south of Nigeria have cut the country's oil output by more than one quarter since the group first emerged in 2006.
Authorities cited in the local media said recent attacks did not have much impact on output levels, which they insist remained around two million bpd.
Author: Jo Amey
