The amount of illegal stimulants smuggled into Japan and impounded by customs officials in 2012 increased 20 percent from a year earlier to around 480 kg, marking the highest level in 10 years.

The number of cases involving impounded stimulants in excess of 5 kg rose to 17 from nine in 2011, the Finance Ministry said Monday.

But the number of cases in which law enforcement authorities took action declined by 24 percent to 141. Cases involving smuggling by people arriving in the country aboard planes, the most common bust, dropped to 84 from a record high 141 a year earlier, but the total amount of drugs impounded as a result stood at 204 kg, the third-highest on record.

Drugs were often concealed in objects ostensibly bought as souvenirs or commercial cargo. There was also a marked increase in the use of airmailed parcels to smuggle drugs, according to the ministry.