VIENTIANE, Jan. 24 (Xinhua) -- A military trainer was killed and 30 students were injured on Tuesday when a hand grenade accidentally exploded during a demonstration of how to properly use grenades at a secondary school in Lao northern Oudomxay Province.

The tragic event happened at the Muaengxay Secondary School in Oudomxay, some 360 km northwest of capital Vientiane, at about 9:00 a.m. local time (0200 GMT), reported Lao state-run news agency KPL.

The KPL quoted a well-known Facebook watchdog site on emerging events in Laos that the military trainer thought that he was using a fake grenade when in fact, he was using a real one during the demonstration.

The military trainer was killed instantly by the explosion which also injured 30 students.

The reason for the mix-up is currently under investigation, said KPL.

Every year in Laos, secondary school students are encouraged to take a one-week military course and higher education students are encouraged to take a military course lasting several weeks.