Nigeria's military say they have found an arms cache belonging to a wanted militant leader in Port Harcourt.
Machine guns, ammunition and dynamite were amongst the haul
The weapons were discovered after a raid on the hide-out of Ateke Tom, the head of the Niger Delta Vigilantes.
The group has been blamed for a spate of recent kidnappings and bank robberies in the oil-rich city.
The BBC's Abdullahi Kaura Abubakar says the find is significant as the group was supposed to have handed in all their weapons after a truce last year.
The Vigilantes, accused of stealing crude oil, were involved in bloody battles with other militants competing for territory in 2004.
Nigeria's military has taken a tough new approach with militants
A reliable military source told our correspondent that four arrests had been made.
But Mr Tom has told the BBC the seized weapons did not belong to him.
The military say their haul included 12 AK47s, seven general purpose machine guns, eight sub-machine guns, ammunition, bullet-proof vests and dynamite.
The abductions and attacks on oil facilities have led to oil companies withdrawing staff, cutting Nigeria's oil production by a quarter.
Foreigners in Nigeria's oil capital, Port Harcourt, now move around with several armed guards.
Oil industry sources say hostage-taking has become an attractive business, as oil companies strike clandestine ransom deals.