Twenty-four civilians have been killed and around 60 wounded in an attack by separatist gunmen in a troubled anglophone region of Cameroon, the local mayor said on Tuesday.

The toll is one of the bloodiest in a nearly five-year-old conflict pitching armed militants against government forces in the breakaway region.

Separatists on Sunday attacked the village of Obonyi II in the Southwest Region near the border with Nigeria, mayor Ekwalle Martin told AFP.

"The separatists wanted the inhabitants to pay them money each month, they refused, and that's why they (the gunmen) attacked," said Martin.

"The toll is 24 dead and at least 62 wounded," he said.

The attack was confirmed by a local administrative official, speaking on condition of anonymity, who gave a death toll of at least 15 civilians.

"After the attack, some people fled into Nigeria and others into the forest," the source said. 

The village, lying 560 kilometres (350 miles) northwest of the national capital Yaounde, "is hard to get to. Armed groups exploit this isolation in order to hand down the law," the source said.

The Southwest Region and neighbouring Northwest Region are home to a large anglophone minority in the majority French-speaking country.

In 2017, anglophone resentment at perceived discrimination radicalised, snowballing into a breakaway movement that declared independence for the two regions. 

The country's veteran president Paul Biya, 89, responded with a crackdown.

Clashes between militants and security forces have claimed more than 6,000 lives and displaced around a million people, according to the International Crisis Group (ICG).

Separatists have targeted police, soldiers, officials and schools, which they deem to be symbols of the state, often carrying out kidnappings.

However, civilians have suffered abuses committed by both sides, according to international NGOs and the United Nations.

Earlier Tuesday, the army said it had freed a kidnapped senator from Biya's Cameroon People's Democratic Movement (RDPC) party.

Senator Elizabeth Regine Mundi, 79, had been abducted along with her driver on April 30 in Bamenda in the Northwest Region.

In an army raid on a "terrorist refuge" in Ashong late on Monday, "several hostages were freed, including the senator," army spokesman Cyrille Atonfack Guemo said in a statement.

He did not provide the exact number of people liberated.

"A dozen terrorists were neutralised, several others wounded and fled. Three were captured," he said. 

Mundi, who hails from the Northwest Region, had appeared shortly after her abduction in a video posted on social media, in which she was shown in front of separatist flags.

Two rebel groups had claimed responsibility for her kidnapping, one of which demanded a ransom while the other demanded the release of prisoners, a senior source in the security forces said.

- Colonial-era legacy -

The presence of the anglophone regions derives from the colonial era.

The former German possession of Cameroon was partitioned after World War I between Britain and France.

In 1961, part of the British territory, the Southern Cameroons, joined Cameroon after it gained independence from France, becoming the Northwest and Southwest regions.

Anglophones have long chafed about perceived inequality, especially in education and law.

The separatists' entity, called the Federal Republic of Ambazonia, has no international recognition.