China's work safety authorities blamed illegal operations for two deadly mine accidents that occurred last month, which together killed 21 people and injured nine others.

Illegal operations and poor management caused the two accidents, one in the northeastern province of Jilin on March 24 and the other in southwestern province of Guizhou on March 28, according to a statement on the website of the State Administration of Work Safety.

The mine in Jilin had been ordered to halt production for safety overhauls but its owner sidestepped inspections and restarted production, while the mine in Guizhou was operating on an expired license when the accident happened.

Meanwhile, both mines had poor management, lacked proper rescue facilities and employed unqualified workers.

The owner of the coal mine in Jilin has been placed in police custody, said earlier reports.

The authorities have pledged to strengthen supervision over coal mine safety in order to prevent deadly accidents, according to the statement.