Hundreds of Bangladeshi left-wing “extremists” will lay down their arms on Tuesday in what police say is the largest surrender of its kind in decades in the South Asian nation.

More than 600 insurgents were expected to turn in homemade weapons and firearms to Bangladesh's home minister and police chief at a formal ceremony at a sports stadium, officials said.

“The government will work to help rehabilitate them so they can return to society,” Sheikh Rafiqul Islam, police chief in the restive northwestern district of Pabna, told AFP.

Bangladesh's western regions have been wracked with conflict since the 1970s until quite recently, with left-wing movements including Maoist outfits and tribal groups fighting the state from jungle redoubts. The country describes them as “extremists” and blames them for the assassinations of political figures and journalists, as well as deadly attacks on the armed forces and police.

Their resistance waned with the formation of Bangladesh's elite police unit in the mid-2000s, which forced the various insurrection movements into retreat through a brutal crackdown.

Rights groups have accused the Rapid Action Battalion police unit of extrajudicial killings of left-wing figures in the country's west and northwest.

Islam said the surrender would be the largest since 1997, when several thousand tribal fighters from the jungle-clad Chittagong hill tracts bordering Myanmar laid down their arms in a peace deal with the government.

Two years later, 400 other militants surrendered and were appointed to Bangladesh's reserve police force. Two months ago, roughly 100 methamphetamine traffickers turned themselves in under an amnesty struck with local authorities.

The government announced a no-holds-barred war on drugs last year to purge Bangladesh of drugs, killing dozens of alleged dealers and methamphetamine kingpins.

Their main target was to curb the smuggling of “yaba”, a cheap and addictive methamphetamine pill trafficked to the country by the hundreds of millions.

Police said 24 “godfathers” were among the traffickers who surrendered in Teknaf, a key border gateway for smuggling yaba into Bangladesh from Myanmar.