in a sign of the growing cross-border threat the militants pose.
The Boko Haram fighters crossed the border into Cameroon earlier this week, after attacking a military base and police station in Nigeria and apparently sending some 480 Nigerian troops retreating across the frontier.
"Cameroon soldiers have killed 27 Boko Haram elements during an attack in a locality near Fotokol in the far north," state radio CRTV said, adding that the deaths occurred on Monday and Tuesday. There was no word on any Cameroonian casualties.
Cameroon borders a part of northeastern Nigeria that has seen intense fighting over the past two weeks.
Boko Haram leader Abubakar Shekau released a video on Sunday showing his heavily armed fighters apparently taking over the hilly Nigerian border town of Gwoza last week, which he declared an "Islamic territory".
It was the first time the militants have made an explicit territorial claim in more than five years of bloody insurgency. They have killed thousands of people since launching an uprising in 2009, but intensified their campaign of violence in Africa's top oil producer in the last year.
In recent weeks, Boko Haram, which is seeking to carve out a de facto Islamic state in northern Nigeria, has stepped up attacks in Cameroon, leading the central African country to increase deployments along its jungle border.
President Paul Biya dismissed two senior army officers last month following attacks in which at least seven people were killed and the wife of the vice prime minister was kidnapped.
A Cameroonian soldier in the region said the militants had been pushed back into Nigeria after the attack on the military base, with calm returning to the area on Wednesday.
A Nigerian security source told Reuters by telephone on Wednesday that the Nigerian military was amassing forces for a counter-attack to push Boko Haram militants out of Gwoza and Gamboru in northeastern Nigeria.
Alice Adejuwon, who fled Gamboru along with hundreds of refugees into Cameroon, told Reuters by telephone that Boko Haram had tried to enter the area to collect bodies of men it had lost, but the Cameroonians forced them back.
"Many of us have fled here," she said, adding that Cameroonian soldiers had supplied some refugees with food. "Boko Haram are still moving around Gamboru so we can't go back."