Nigeria's armed forces on Saturday arrested a militant gang leader and more than 60 of his followers believed to be behind the kidnapping of 19 oil and construction workers in the Niger Delta.
The hostages - two Americans, two Frenchmen, two Indonesians, one Canadian and 12 Nigerians - were freed late on Wednesday after being held by a gang leader known as Obese at a camp in Rivers state.
Obese, 25, whose real name is Tamunotonye Kuna, was paraded with 63 followers in front of the media at an air force base in the southern oil hub of Port Harcourt.
Five AK-47 assault rifles, 12 machineguns, ammunition, bullet-proof vests, military-style fatigues, boots and badges with the logo of the militant Movement for the Emancipation of the Niger Delta (MEND) seized from his camp were also on show.
Obese was one of thousands of gunmen who signed up for an amnesty brokered last year by President Goodluck Jonathan.
Dressed in a tracksuit and flip-flops, he told reporters he was a MEND commander who had grown disillusioned with the amnesty because, unlike his former leaders, he had seen no benefit from the programme.
"I went back to the creeks because I did not like the way some of our leaders are [behaving]" he said. "We are supposed to hear from our masters to know what is happening, the way the government is [dealing]with them, but I never heard anything. That's where the mistake is."
Resurgent unrest in the Niger Delta risks undermining the credibility of President Jonathan in the run-up to elections next April. He is the first head of state from the oil region and the amnesty was considered one of his key achievements.
Key MEND field commanders, including Obese's former gang leader Farah Dagogo, accepted last year's amnesty and received significant payments for doing so, security sources say.
Thousands of their followers have been through a re-orientation programme meant to teach them about non-violent protest, but unemployment is rife and many remain frustrated at the lack of economic opportunity.
Mr. Dagogo was instrumental in persuading Obese to hand over the 19 hostages, security sources have said.
The armed forces have said they have taken over several militant camps in the Niger Delta, the heartland of Africa's biggest oil and gas industry, and will carry out more raids to flush out gang members.
Previous campaigns by MEND fighters have knocked out a significant chunk of Nigeria's oil production, currently averaging around 2.2 million barrels per day (bpd), and cost it as much as $1-billion a month in lost revenues.
MEND has threatened further attacks, but security experts believe the amnesty and the arrest of some key militant leaders have damaged the group and made major unrest unlikely at this stage.
It remains impossible to guard oil facilities fully against sabotage and piracy.
Shell declared force majeure on its Bonny Light oil exports on Friday after a pipeline was damaged, freeing it from shipment obligations, though there was no immediate evidence of links to militant activity.
Oil infrastructure in the delta, a network of thousands of shallow creeks opening into the Gulf of Guinea, is extremely exposed with thousands of kilometres of pipeline passing through remote and thickly forested terrain.
Disputes between local communities and oil firms are common, and attacking a pipeline and shutting down production requires little more than simple home-made explosives.
It is also extremely difficult to protect offshore platforms such as those operated by Exxon Mobil and Afren, from where 15 of the 19 hostages were kidnapped.
The militants use open craft too small to be detected by radar for such raids and are even able to operate far offshore by using a "mother ship," a larger vessel which supplies the speedboats with fuel and food, security experts say.