Nigeria's President Muhammadu Buhari said he ordered a heightened military presence in the restive Niger Delta region to deal with a resurgence of attacks on oil and gas facilities, a day after yet another pipeline explosion.
British Foreign Minster Philip Hammond warned on Saturday military action would not end a wave of attacks in the southern swamps because it did not address rising anger among residents over poverty despite sitting on much of Nigeria's oil wealth.
The rise in attacks in the Delta in the last few weeks has driven Nigerian oil output to a more than 20-year low, worsening a drain on public finances.
A group calling itself the Niger Delta Avengers has claimed responsibility for several sophisticated attacks.
Speaking at a meeting with Shell's upstream head, Andrew Brown, Buhari said he had instructed the chief of naval staff to reorganize and strengthen the military Joint Task Force to deal with the militancy.
"We have to be very serious with the situation in the Niger Delta because it threatens the national economy," Buhari said in a statement.
"I assure you that everything possible will be done to protect personnel and oil assets in the region," he added.
Nigeria had several times announced army reinforcements to the Delta but diplomats said the military has achieved little as militants were operating in small groups and hiding in the hard-to-access swamps.
"Mr. Brown had appealed for an urgent solution to rising crime and militancy in the Niger Delta," the presidency said.
An industry source told Reuters that major oil firms warned Vice President Yemi Osinbajo this month that a military crackdown was actually fuelling dissent in the Delta.
The presidency statement also quoted Brown as saying Shell would not pull out of Nigeria despite the violence and that it was in talks with state energy firm NNPC for new oil and gas projects.
Their was no immediate comment from Shell, but its country chair said in an interview published on Sunday the firm was committed to long-term investment in the West African nation.
Buhari's comments came after locals said a gas pipeline operated by NNPC was attacked late on Thursday.
The pipeline, which connects the Escravos oil terminal to Warri, supplies gas to different parts of the country.
Eric Omare, a spokesman for the Ijaw Youth Council, a youth umbrella, said the attack occurred near the village of Ogbe Ijoh, near Warri, "on the pipeline belonging to NNPC.
Resident James Dadiowei said he heard a "loud bang" at the pipeline, but an NNPC spokesman was unable to confirm the attack.
On Thursday, intruders blocked access to Exxon Mobil's terminal exporting Qua Iboe, Nigeria's largest crude stream. And, earlier this month, Shell workers at Nigeria's Bonga facilities were evacuated.
In February, the Avengers claimed an attack on an undersea pipeline, forcing Shell to shut a 250,000 barrel-a-day Forcados terminal.
The group also claimed responsibility for blasting a Chevron platform in early May, shutting the Warri and Kaduna refineries. Power outages across Nigeria worsened as gas supplies were also affected.
The army said on Sunday it had arrested several suspected members of the Avengers, but locals said they had been freed.
"They were released on Wednesday evening," Omare said.
Residents said the military had described them as Avengers but locals had protested they were Chevron pipeline inspectors who had shown the soldiers arresting them their identity cards.
Militant attacks have spiked since authorities issued in January an arrest warrant for a prominent former militant leader who with other rebels in 2009 agreed to stop blowing up pipelines in exchange for cash, a plan Buhari has trimmed as part of an anti-graft drive.