Three people have been detained in Belgium as part of a probe into possible crimes against humanity and war crimes in Cameroon linked to the country's secessionist rebellion, Belgian prosecutors say.

They are suspected to be leaders of the Ambazonia Defence Forces (ADF), a militia fighting for the independence of Cameroon's two Anglophone regions in what is a mainly French-speaking nation.

"Money is reportedly being raised for the armed struggle and for the purchase of arms and ammunition, and instructions for attacks… are said to be given from Belgium," the federal prosecutor's office said.

The UN says more than 6,500 people have been killed since the conflict began nearly a decade ago.

Separatist fighters in the country's two English-speaking regions - the North-West and the South-West - took up arms in 2017 calling for the creation of a breakaway state called Ambazonia.

Human rights groups have accused both the rebels and state forces of committing widespread abuses.

According to the Belgian prosecutors, four people were arrested on Sunday and followed co-ordinated searches in the city of Antwerp and in the Flemish town of Londerzeel.

''Three of the suspects were remanded in custody by the investigating judge," the office of the prosecutor said in a statement.

It added that its investigation had been launched last summer into individuals living in Belgium who were suspected of being part of the leadership of the ADF.

The arrests in Belgium follow similar investigations in both Norway and the US.

Cameroon's Anglophone crisis began in 2016 when lawyers and teachers went on strike over the use of French in courts and schools.

When activists - angered by what they saw as the marginalisation of Cameroon's minority Anglophone community by the Francophone-dominated government -declared the independent state of Ambazonia a year later, it triggered the conflict involving groups such as the ADF.

According to the UN, the unrest has forced more than 490,000 people from their homes, left more than 1.5 million in need of humanitarian assistance and thousands dead.

President Paul Biya, who has ruled Cameroon for more than 40 years, says his government has made significant efforts to resolve the conflict.

But his administration continues to draw criticism over its handling of the situation and its restrictions on political freedoms in the country.