BEIJING, Feb. 17 -- Chinese police have arrested over 20,000 suspects in their crackdown on online drug-related crimes since 2011, the Ministry of Public Security announced on Tuesday.

Police have launched four rounds of operations over the last four years and seized 1.56 tonnes of narcotics and 7.83 tonnes of precursor chemicals.

A total of 24 production sites have been shut down and 40 guns and 1,710 bullets were seized.

The total sum of money involved in these cases reached 354 million yuan (56.6 million U.S. dollars), the statement said.

The statement noted that more drug-related crimes are originating online, accelerated the spread of drugs.

The ministry said police had dealt with thousands of pieces of online content relating to drug crimes. It also said that some Internet operators had failed to play their part in the crackdown.