Ethnic Kachin rebels in Myanmar, also known as Burma, say the government has attacked their headquarters and military training school, killing nearly two dozen cadets.
Kachin Peace Negotiator Hkun-Ja tells VOA's Burmese service the surprise artillery attack came from a tall hill outside the northern town of Laiza, which is home to the Kachin Independence Army (KIA).
"Twenty KIA military cadets were killed and 16 others wounded. Another front line post of KIA Battalion 26 at Mai-Lao area was also under attack and destroyed today at about 3 a.m.," said Hkun-Ja.
At least one other Kachin camp was under fire Wednesday. The government and military have not commented on the attacks.
Hkun-Ja says the resumption of stalled ceasefire talks between two sides is now uncertain due to the government offensive.
The Kachin and several other ethnic rebel groups have been fighting the central government for decades, leading to the deaths of tens of thousands of people.
Most of the groups have signed temporary ceasefire agreements in recent years, but permanent peace deals are still being discussed.
This report was produced in collaboration with the VOA Burmese service.