Troops from Chad and Niger have retaken the northeastern Nigerian town of Damasak as part of regional efforts to combat the Islamists who have pledged allegiance to Islamic State militants.
Boko Haram had held the town near the Niger border since November, part of a swathe of territory it had taken over in Nigeria's northeast, where the group's six-year insurgency has been based.
"The offensive has allowed for control to be taken of Damasak," a Chadian security source said on Monday.
According to the source, some 200 Boko Haram fighters were left dead in the offensive that began Sunday, while 10 Chadian soldiers were killed and 20 wounded.
There was however no independent verification of the casualty figures. A hospital source in Niger's Diffa, across the border from Damasak, spoke of 33 soldiers wounded, without providing their nationalities.
A Niger official in Diffa also said Damasak had been retaken after heavy fighting.
The offensive, which followed a sustained build-up of troops in southern Niger, opened up a new front in regional efforts to wipe out the Islamist group, whose six-year insurgency has spread across borders.
It also came after Boko Haram leader Abubakar Shekau pledged allegiance to the Islamic State group in Iraq and Syria in an audio message at the weekend.
More than 200 vehicles, some of them with machine guns, as well as tanks, ambulances, water tankers and transport trucks, were seen moving towards the border on Sunday, Diffa-based radio station Anfani reported.
Aircraft targeted Boko Haram positions on Saturday and early Sunday, it added, while a Diffa resident and aid worker said Sunday that troops were seen heading to the border and heavy gunfire was heard.
More than 13,000 people have been killed and some 1.5 million made homeless in the Boko Haram conflict since 2009, and the regional coalition was prompted by security fears following cross-border attacks.
On Friday, the African Union endorsed the creation of an additional regional force of up to 10,000 men to join the fight against Boko Haram.
The regional coalition already operating has given renewed vigour to the previously lacklustre counter-insurgency against Boko Haram.
The armies have claimed a series of successes in rebel-held territory in recent weeks, as part of an operation to clear and control northeast Nigeria in time for Nigeria's general elections set for March 28.
Much of the focus has been on Chad's well-trained army, who have experience in tackling Al-Qaeda-linked extremists in Mali alongside French forces.
But Chris Olukolade, spokesman for the Nigerian military, has said the Niger and Chad assaults were "complementary to (Nigeria's) ongoing push against the terrorists".
Nigeria's military did not respond to messages on Monday.
With Shekau's pledge of allegiance to the Islamic State at the weekend, the Nigerian militants joined extremists from Libya to Pakistan who have previously done the same.
While some saw it as a propaganda stunt, there were also concerns about whether the move could eventually lead to deeper links between Boko Haram and foreign jihadists.
Some experts also said the pledge of allegiance to IS, which is also being forced on the defensive in Iraq, could be a result of the military pressure.