The Narcotics Control Bureau (NCB) has suspended two of its Mumbai zone officers, superintendent V V Singh and intelligence officer Ashish Ranjan Prasad, for alleged "dereliction of duty" in investigations conducted by them, officials said on Wednesday.

The two officers also investigated the cruise drugs case in which at least 20 people, including actor Shah Rukh Khan's son Aryan Khan, were arrested in October in Mumbai. Singh was the investigating officer of the case and Prasad his deputy.

However, officials said, their suspension was not linked to the cruise drugs case which led to a controversy after allegations of procedural lapses and extortion were made against the sleuths by an independent witness, Prabhakar Sail, who recently died from heart attack.

Senior officials told PTI that Singh and Prasad have been placed under suspension for alleged "dereliction of duty" in investigations conducted by them in the NCB zonal office in Mumbai. The orders for their suspension were approved by NCB director general S N Pradhan on the basis of a report and recommendation made by the zonal director or head of the NCB unit in Mumbai and regional director (deputy director general south-west) Ashok Mutha Jain.

The NCB is the apex agency against drug-related crimes in the country.