Ethnic Kachin rebels in northern Myanmar say the army has killed 22 of their fighters in a mortar attack near the Chinese border.

A spokesman for the rebel Kachin Independence Army, La Nan, said the attack took place Wednesday close to the rebel headquarters in Laiza.

He said the army fired from a nearby hilltop and hit a rebel officer training academy, killing 22 people and wounding 15 others.

Myanmar's government could not immediately be reached for comment.

Fighting between the army and Kachin insurgents broke out in 2011, ending a 17-year truce.

President Thein Sein's government has agreed to tentative peace deals with 14 insurgent factions since then, but has not been able to secure a wider deal encompassing all armed groups.