|Attacks raised fears that MEND's violent campaign to disrupt oil production is resuming after a two-year hiatus [EPA]
A group fighting for a greater share of Nigeria's oil wealth in the country's delta region has claimed responsibility for killing four police officers this week.
The Movement for the Emancipation of the Niger Delta (MEND) said in an email it sent to reporters on Friday that it shot the four police officers who were on a boat patrolling the Nembe river in Bayelsa state on Thursday.
The attack is the second assault in about four weeks.
The police attack comes about a month after MEND claimed responsibility for an attack on an oil pipeline in the area that is operated by Italian firm Eni SpA.
Before the recent pipeline attack, the group had been relatively quiet.
The two attacks raise fears that MEND, which once crippled Nigeria's oil industry with a wave of attacks targeting foreign oil companies, could be remobilising.
The statement also raises concerns about MEND's ties with pirates.
The group said said in the statement that kidnappers of three foreign crew members on a Dutch-owned vessel had offered to hand over their hostages to MEND. It said the hostages were in good health.
The International Maritime Bureau had reported that a captain and chief engineer were kidnapped off the vessel anchored in the city of Port Harcourt during an attack by pirates on Tuesday. It said a crew member was also missing.
The Curacao-flagged vessel laden with refrigerated cargo had 14 crew members from Russia, Ukraine and the Philippines, said Noel Choong, who heads the bureau's piracy reporting centre in Kuala Lumpur.
Choong did not give the kidnapped crew members' nationalities.
The MEND statement named the hostages and said the captain and chief engineer are Russian, while the crew member is from the Philippines.
"We are considering this offer [to take over the hostages] as these men were not captured from a vessel related to the Nigerian oil industry," the statement read. It did not say what was required for the hostages to be freed.
"We are studying the statement," said Lieutenant-Colonel Timothy Antigha, spokesman for a special taskforce dealing with the threat of militancy in the oil-rich region. "We have learned to take these claims with a pinch of salt."
MEND started its violent campaign in 2006 in Nigeria's southern delta, where foreign firms have pumped oil out of the country for more than 50 years.
That violence ebbed in 2009 with a government-sponsored amnesty program promising ex-fighters monthly payments and job training.
But few in the delta have seen the promised benefits and scattered kidnappings and attacks continue, though at much smaller scale than they used to occur.