Nigerian militants said on Sunday they had blown up two oil and gas pipelines in the Niger Delta in response to military gunboat and helicopter strikes which rights groups say have displaced thousands, Reuters reported.
The army said it had clashed with militant fighters again on Sunday at Kunukunuma in Delta state as it tried to flush the rebels out from their camps deep in the creeks. It warned it would continue with its operation until it succeeded.
The Movement for the Emancipation of the Niger Delta (MEND) said it had sabotaged two oil and gas pipelines near to Escravos which supply the 110,000 barrels per day (bpd) Kaduna refinery in northern Nigeria, shut down for maintenance in November.
There was no immediate independent confirmation.
"We have begun nibbling again at the oil infrastructure. Already, two major trunk pipe and gas lines which were recently repaired have been blown up," MEND said in an e-mail to media.
A private security contractor said there were also reports of an explosion overnight at a manifold operated by Royal Dutch Shell's local unit in neighboring Bayelsa state. Shell said it was checking but had no immediate confirmation.
Local rights groups said the military's use of helicopter gunships in recent days had triggered a "mass evacuation" of villagers and urged restraint by the security forces. It asked both sides to allow humanitarian access to those displaced.
"There is no doubt that there are casualties from the current clashes who need urgent medical attention and there are thousands more who have fled their villages," three local rights groups said in a joint statement.
Reuters reporters saw dozens of displaced villagers sheltering in Ogbe-Ijoh hospital on the outskirts of Warri, the nearest main town.
Insecurity in the Niger Delta means the OPEC member's oil output, currently around 1.9 million bpd, is running at less than two-thirds capacity, curbing foreign revenues and putting an additional strain on government finances.
Global crude oil markets have largely ignored the clashes in the OPEC member country, closing lower in two of the last three sessions.
The military has said it cannot "fold its hands" while the country's mainstay industry is under threat.
"In continuation of our search-and-rescue operation this morning in Kunukunuma, our troops encountered resistance from militants," military spokesman Colonel Rabe Abubakar said.
"The operation continues until we flush out the criminals we are looking for," he said.
Sunday's clashes follow helicopter and gunboat strikes on Friday against a major militant camp after the hijacking of two oil vessels and kidnapping of crew members.
The army said it had rescued nine Filipino and four Nigerian hostages in the operation and destroyed the camp belonging to Government Tompolo, a leader of a faction of MEND known as the Federated Niger Delta Ijaw Communities (FNDIC).
The rescued crew members told reporters on Saturday that two Filipinos were killed and at least five others wounded by crossfire. MEND said Tompolo had survived the assault and that his fighters had relocated to another camp.
"FNDIC fighters will likely counter-attack Nigerian army positions and target pipelines and flow stations in Delta state in order to press the Nigerian government to rein in its armed forces," risk consultancy Stratfor said on Friday.
MEND said it had moved Matthew Maguire, a British oil worker held hostage since last September, to Delta state, the scene of the latest fighting. Maguire had previously been held at a camp in neighboring Rivers state.
The group has in the past used foreigners as "human shields" in an attempt to discourage the military from using force.