Cameroon's President Paul Biya said he will drop charges against 333 prisoners arrested for their alleged roles in a two-year separatist uprising.

The announcement on Twitter on Thursday comes during peace talks launched by Biya to end fighting between insurgents and the military that has killed more than 1,800 people, displaced over 500,000 and put a major dent in the economy.

Rebel leaders dismissed the move as a political stunt and pledged to keep fighting.

But Thursday's move represented one of Biya's largest concessions yet amid what has become a major threat to his near 40-year rule.

"I have ordered the discontinuance of proceedings pending before Military Tribunals against 333 persons arrested for misdemeanours, in connection with the crisis in the North-West and South-West Regions," said Biya on Twitter.

Anglophone separatists, who are trying to form a breakaway state called Ambazonia in the majority French-speaking country's two minority English-speaking regions, on Thursday said that the amnesty did not go far enough.

The separatists have called for the release of what they say is 5000 people imprisoned since 2016, including 10 leaders who were sentenced in August to life in prison on terrorism charges, and the withdrawal of Cameroon's military from the North-west and South-west regions.

"We will not accept an olive branch from someone whose troops are still in our territory," said Ivo Tapang, a spokesman for 13 armed groups called the Contender Forces of Ambazonia. "We will intensify our struggle with guns and bullets.”

The insurgency emerged after a government crackdown on peaceful protests late in 2016 in the Northwest and Southwest regions by lawyers and teachers who complained of being marginalised by the French-speaking majority.