Boko Haram have seized a strategic town in Nigeria's far northeast, prompting denials from the military, as experts said the government risked losing control and the region was "on the brink" of takeover.
Residents in Bama and a local politician said on Tuesday that 400 troops, some of them without weapons or boots, had fled after a military jet mistakenly bombarded the town's barracks during intense fighting.
Nigeria's military countered that it had pushed back the militants, who in recent weeks have moved from indiscriminate and retaliatory hit-and-run attacks to seizing strategic territory in Borno state.
However, Ali Ndume, a Nigerian senator, said thousands of people were seen fleeing Bama, contradicting the military's claims that they had repelled an attack on the town.
Last week, fighters, blamed for killing thousands since 2009, overran the border town of Gamboru Ngala and previously seized Gwoza and declared it part of an Islamic caliphate.
Nigeria is losing control of large parts of the northeast region
Some analysts have predicted that by seizing territory, Boko Haram is seeking to encircle the state capital, Maiduguri, 70km away, to make it the centre of an Islamic state.
"Nigeria is losing control of large parts of the northeast region," said Andrew Noakes, of the Nigeria Security Network of experts in a report that warned of potential knock-on effects.
It would be a major victory for the fighters if Boko Haram has seized Bama, the second largest city in Borno state.
Establishing control over Bama would leave the way open to attack the Borno state capital of Maiduguri that is also the military headquarters of the fight against Boko Haram.
"If Borno falls to Boko Haram, parts of [neighbouring] Yobe and Adamawa [states] can be expected to follow. Parts of Cameroon along the border area would also probably be overrun," Noakes said.
On Tuesday, Cameroon's army claimed to have killed more than 40 Boko Haram fighters who tried to storm a strategic border crossing.
Heavily armed fighters "attempted to cross the bridge at Fotokol" in the extreme north of the country and opened fire on Cameroonian soldiers, the ministry of defence told state radio.
There was no independent confirmation of the battle.