Police arrested Abiodun Amos, the suspected leader of a "militant gang", on November 2 after "painstaking surveillance and monitoring," national police spokesman Don Awunah said in a statement late yesterday.
Authorities suspect the target was the 13-kilometre 3rd Mainland Bridge, which links the swanky business district of Lagos Island with the rest of the sprawling city of some 20 million inhabitants.
The attack would have caused "devastating" damage to Lagos and Nigeria, Awunah said.
Information obtained from Amos led police to other plot members and they found two cartons of explosives and 125 detonators in the boot of a car as the alleged conspirators were en route to the bridge.
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Police were now trailing fleeing members of the gang, he added.
Lagos, Nigeria's largest and commercial hub, has been on security alert following rumours of militant attacks in recent months.
Nigeria's oil-producing south has been plagued by renewed rebel attacks on oil pipelines and facilities that have crippled output at a time of global low prices, hammering government revenue.
Nigeria depends on oil for 90 per cent of foreign exchange earnings and 70 per cent of government revenue.