They were being arrested two months ago in an apartment they had rented from a retired police official.

The official, a former regional chief of the Central Bureau of Investigation, Upen Biswas, was not mentioned in the charges filed against three Burmese, two Chinese and two Indian nationals.

They are said to be members of a notorious drug gang based in southwest China's Yunnan province.

A BBC correspondent in Calcutta says Mr Biswas, who's being treated as a witness in the case, is a highly respected policeman who relentlessly prosecuted Bihar's former chief minister, Laloo Prasad Yadav.