One officer was killed when an improvised explosive device seized from Boko Haram Islamists detonated at a police station in northeast Nigeria, a force spokesman said on Thursday.
"There was an accidental explosion in an armoury manned by our bomb squad," Adamawa police spokesman Othman Abubakar told AFP from the state capital, Yola.
The device "killed one officer and mildly injured others", he added, without specifying numbers.
"Contrary to speculation, the explosion had nothing to do with any sabotage or attack. We have recovered lots of explosives from these troubled areas.
"Usually we screen them and store them for safe-keeping. We don't know what happened. Possibly this wasn't screened properly," he added.
The Nigerian Red Cross and the country's National Emergency Management Agency (NEMA) said earlier they were responding to a bomb blast at the police station in the Jimeta area of Yola.
Aliyu Maikano, an official with the Nigerian Red Cross, said the blast "wrought massive destruction on the building" and sparked a fire.
"We've been told by security personnel that there are two more explosives that are yet to detonate," he added.
"All rescue respondents are staying outside from a distance waiting for a signal from the security agents to go in and start rescue operations."
The blast, which happened at 11:30 am (1030 GMT), sparked fears of another attack by Boko Haram, which has targeted the city before as well as police stations and government buildings across the northeast.
On November 17 last year, at least 34 people were killed and 80 others injured when an IED went off at a lorry park in the Jambutu area of the city.
At least 27 people were killed and 96 wounded in a blast at a Jambutu mosque on October 23.
Another home-made bomb left at a camp for people displaced by the conflict in Malkohi, just outside Yola, killed seven on September 11.
The insurgency has left at least 17,000 people dead since it began in 2009 but over the last year a sustained counter-insurgency has recaptured territory lost to the rebels.
The group has since reverted to attacks on "soft" civilian targets such as markets, bus stations and mosques using suicide bombers and IEDs.