Human rights groups said the conflict between Myanmar's military and the Kachin Independence Army escalated during the last two years, forcing large numbers of civilians from their homes and into refugee camps either in the state or across the border in China.
U.S. officials said they were "deeply troubled" by Myanmar's admission that it used air attacks on the rebel forces this week.
"We're obviously deeply troubled by the increased violence," U.S. State Department spokeswoman Victoria Nuland said Wednesday. "We are continuing to urge the government of Burma [as Myanmar once was known] and the Kachin Independence Organization [KIA's political arm] to cease this conflict, to get to a real dialogue to address grievances as the government of Burma has been able to do in virtually all of the other conflict areas."
Nuland said Kachin, along with Rakhine state, is "where we're still seeing difficulties. And we have consistently raised our concerns about violence in Burma's ethnic minority areas."
In the past year, the Myanmar government has progressed in peace talks with minority groups, including securing a cease-fire with separatist Buddhist Karen rebels, CNN reported Thursday. However, clashes between Buddhists and Muslims in Rakhine triggered a humanitarian crisis and pointed up the difficulty in addressing Myanmar's ethnic mix amid new political freedoms.
The Myanmar military has been using "air cover" in Kachin since Dec. 27 to transport supplies to a base near Laiza, Kachin's capital and KIA headquarters, presidential spokesman Zaw Htay said.
The air attacks were Sunday and Monday, he said.