Cameroon has sent warplanes into action against Nigerian Boko Haram fighters for the first time, after the large force of jihadists crossed the border and seized a military camp, the government said.
President Paul Biya personally ordered Sunday's air strike, which forced the insurgents to flee the camp at Assighasia, Communications Minister Issa Tchiroma Bakary said in a statement late Sunday.
"Fighter planes went into action for the first time since the start of the conflict" on the Cameroonian side of the frontier, after several months of deadly cross-border Boko Haram raids, Bakary added.
"After two strikes and heavy fire... the assailants fled the Assighasia camp... losing several fighters," he said.
Military operations were still under way, he added, saying that "the toll from combat will be released once the operational evaluation is complete".
The extremists of Boko Haram, which roughly means "Western education is forbidden", have made frequent raids into neighbouring Cameroon since they began their insurgency in northern Nigeria in 2009.
Boko Haram tactics include massacres of civilians on both sides of the frontier, bomb attacks on state institutions and schools, and the razing of villages and mass kidnappings.
Since early in 2014, the movement has sent growing numbers of fighters into Cameroon, prepared to battle the army head-on as well as attacking and intimidating villagers.
On October 15, Boko Haram forces equipped with a captured tank and an armoured vehicle attacked a military base at Amchide, near the border, in a raid that killed several dozen civilians and eight soldiers, according to officials.
Several hundred Boko Haram fighters assaulted the Assighasia camp early on Sunday, so that "Cameroonian defence forces had to withdraw after trying to defend the position", the government said.
The air strikes marked "a new escalation in the Cameroonian response... to multiple enemy attacks by the Boko Haram terrorist group," the statement said, but it also sent a signal to other countries.
Cameroon's neighbours, together with former colonial power France, have long criticised the authorities for what they considered a passive response to the actions of the jihadist movement even as its members used Cameroonian territory to rest and buy food and weapons.
When a French family was kidnapped in 2013, along with two Italian priests and a Canadian nun, President Biya sent major army reinforcements to confront the Islamists in "Operation Alpha". The hostages were freed this year in Nigeria.
Some 2,000 Cameroonian troops patrol the far-north region, but security sources say that many more are needed because the area is so remote with a very porous border.
Military sources accuse Nigeria's army of failing to do enough against jihadist forces who have taken control of large swathes of the northeast of the country.
"Attacks on our territory come from a neighbouring country that calls itself sovereign and does nothing," a defence ministry official in Yaounde recently told AFP, asking not to be named.
Backed by France, Nigeria and three nations on its northern border -- Cameroon, Chad and Niger -- agreed on measures in May to help tackle the Islamist threat, including pooling intelligence, joint border surveillance and an intervention force.
Each of the four countries agreed to send 700 soldiers to the Lake Chad region where their frontiers meet.
"Cameroon has already sent 300 men from the navy to the region," an army officer told AFP late in November. "Chad and Niger are well placed to send troops, but that's less certain where Nigeria is concerned."