HOHHOT -- Police in North China's Inner Mongolia autonomous region have nabbed four suspects and seized narcotics and drug-making materials, after uncovering a drug manufacturing case.

The police operation in Huade County started after they monitored two suspects who were engaged in the drug trade. Police seized 28 kg of caffeine and 24 kg of caffeine sodium benzoate on the spot.

Through an interrogation of the suspects, police found the drugs came from a local underground drug-making workshop. A raid was soon launched leading to the seizure of 131 kg of sodium benzoate and 23 kg of caffeine on the spot.

Police are still probing into the case.