Myanmar’s military has acknowledged that it launched airstrikes against ethnic Kachin rebels in the north of the country, contradicting claims made two days earlier.

It also said in a televised statement that it had captured a post in the hills from which the insurgents had attacked government supply convoys, reports AP.

There are increased doubts over how much control the elected government of President Thein Sein, a reformist, has over the army, with a statement from Washington saying the airstrikes were “extremely troubling.”

U.N. Secretary-General Ban Ki-moon called on Myanmar’s authorities “to desist from any action that could endanger the lives of civilians living in the area or further intensify the conflict in the region,” and called on the government and rebels to work toward political reconciliation, U.N. spokesman Martin Nesirky said.

The Kachin Independence Army had been issued an ultimatum by the government which had told it to clear a road on Christmas Day. The KIA said, though, that it had rejected that for fear of attack.

KIA spokesman La Nan alleged Monday that supplies the road was to be cleared for were meant for government troops and included ammunition as well as rice.

“We will obstruct any army convoy that carries arms and ammunition that will be used against us,” he said. “This is the nature of war.”

The The Kachin, like Myanmar’s other ethnic minorities, have long sought greater autonomy from the central government but are blamed by some in an ongoing war-of-words for violence in the northern region.