Efforts at negotiation between the government and the Kachin ethnic group appeared to have stalled as fighting was reported near Kachin headquarters, The New York Times said.
"The fighting is intensifying now," a Catholic priest returning from the area told the Times. The priest, whose name was not reported, said Kachin fighters had begun guerrilla attacks against the military.
The priest said some clergy were trapped in the region by the clashes and tens of thousands of villagers have fled to refugee camps near the Chinese border.
There is a long history of conflict in Myanmar -- formerly called Burma -- between the government and ethnic groups, which make up about one-third of the country's population of 55 million, the newspaper reported.
"The ethnic people of this country have different backgrounds, different histories, different cultures -- even different ways of naming their children," Yogawng Hawng Hkawng, 88, a Kachin Baptist minister, said in an interview this year. "We are different clans. Because of those differences, I don't see the country ever being peaceful. There will always be problems, one way or another. I don't think the country can be united."