Boko Haram extremists have attacked a Nigerian border town, killing 11 people who had recently come home after military forces ousted the insurgents, witnesses said.
Resident Mohammed Umara said Cameroonian forces immediately crossed the border when gunfire erupted and drove the militants from Gamboru-Ngala.
"We were terrified when we started hearing gunshots echoing ... but everywhere became calm about an hour later. The soldiers informed us that it was the Boko Haram terrorists that came back," said another resident, Aji Kaumi.
He and Mr Umara said 11 civilians were killed on the outskirts of Gamboru.
They and other fearful residents crossed back to the relative safety of the Cameroonian town of Fotokol.
It was the first reported attack on a town previously occupied by Boko Haram since a regional offensive was launched by troops from Chad seven weeks ago. Nigerian officials this week said they had taken back 38 north-eastern towns and forced Boko Haram out of two states and most of Borno state.
The extremists seized Gamboru in November and were dislodged on February 4.
The offensive comes as Nigerians prepare for a closely contested March 28 presidential election.
Nigeria says the multinational military effort aims to eradicate Boko Haram, but a French diplomat says a more realistic goal is to reduce Boko Haram to what it used to be - an extremist group holding no territory.
France brought about the regional co-operation with a summit in Paris last year that eased strained relations between Nigeria and its smaller, francophone neighbours amid growing concern as Boko Haram began launching attacks across Nigeria's borders.
France has sent military advisers to Niger and its Chad-based aircraft are on scouting missions to help the effort.
The death toll from the nearly six-year Islamic uprising mounted exponentially last year with 10,000 people killed and more than 1.5 million driven from their homes, according to the US-based Council on Foreign Relations.