Nigeria has warned civilians that Boko Haram is using deadly cluster bombs but campaigners say the Islamists may have got the banned weapons from the military in the first place.
Defence spokesman Rabe Abubakar urged people to be on their guard for "cluster bombs, sometimes scalled scatter bombs", as engineers had recently found caches in northeastern Adamawa state.
"The military high command has discovered that the Boko Haram terrorists in the areas have used such lethal instruments over time to push their callous terrorist cause," he said last Thursday.
"These bombs are used against large areas containing many targets such as columns of vehicles, marketplaces, places of worship or large troop concentrations," he added in a statement.
The insurgents, allied to the Islamic State group in Syria and Iraq, have in recent months increasingly used suicide and bomb attacks in northeast Nigeria, Chad, Cameroon and Niger.
Abuja has described the attacks, which have caused mass civilian casualties, as desperate acts following apparent army gains in the northeast when soldiers overran their training camps, and hundreds of fighters allegedly surrendered.
Cluster bombs are a category of ordnance dropped from planes or fired from artillery via a shell, missile or rocket and spread hundreds of tiny sub-munitions or "bomblets" over a wide area.
Many of the devices fail to explode on impact and effectively become de facto landmines hidden for years, making them difficult to clear and posing a significant risk to civilians.
More than 100 countries signed the UN Convention on Cluster Munitions that came into force on August 1, 2010 banning the use, production, transfer and stockpiling of cluster munitions.
Nigeria has signed but not ratified the convention and the Cluster Munition Coalition (CMC) campaign group said Abuja had still to declare its stockpiles and detail how it would get rid of them.
Photographs posted on the Nigerian Defence Headquarters Twitter feed suggested the bombs were sub-munitions for the French-made BLG-66 Belouga, normally launched from aircraft, the CMC said.
