Cameroonian paramilitaries have crossed into neighbouring Nigeria to conduct operations among citizens who have fled from Cameroon's restive anglophone regions.
State sources made the announcement yesterday.
John Inaku, the head of Cross River state emergency management agency, confirmed local press reports that gendarmes were in Danare village in the Boki area of the state early on Monday.
"There were people coming in from the neighbouring country. It is not the first time. The first time was in (the district of) Ekang in December," he told AFP.
A police source in the south-east Nigerian state said only: "Yes, it's true. There were men on the ground."
Thousands of Cameroonians have fled to the remote region from violence in English-speaking south-west Cameroon, which abuts Nigeria.
Paramilitaries came in from Cameroon targeting suspected anglophone separatists among the influx, Nigerian media said yesterday.
Cross River state security adviser Jude Ngaji was quoted as saying by The Punch newspaper: "The issue has gone beyond the police and the Nigerian Army has just deployed a battalion to the area."
Cameroon's government is fighting an insurgency by a group demanding a separate state for two regions that are home to most of the country's anglophones, who account for about a fifth of the population.
On October 1 last year, the breakaway movement issued a symbolic declaration of independence for "Ambazonia," their name for the putative state.
Cameroon's President Paul Biya has met the agitation with a crackdown, including curfews, raids and restrictions on travel. Around 30,000 people have fled into neighbouring Nigeria.
Despite their military collaboration against Boko Haram Islamists in north-east Nigeria and northern Cameroon, the two countries have long had tense relations.
For years, the neighbours staked claims to the oil-rich Bakassi peninsula until an International Court of Justice ruling ceded it to Cameroon in 2002.
Nigeria is also facing an independence movement from pro-Biafran supporters in the south-east but Abuja has moved closer to Yaounde in recent weeks.
On Monday, the head of the Ambazonia separatist movement, Sisiku Ayuk Tabe, arrested in the Nigerian capital in early January, was extradited with 46 supporters.
Yaounde has called them "terrorists".
