BANGKOK -- Myanmar admitted on Wednesday that it was using aircraft to attack rebels near the border with China, a development that the United States described as an "extremely troubling" escalation of the conflict.
Ethnic Kachin rebels, who are battling the government for control over the northern areas of the country, have in recent days reported being attacked by helicopters and other aircraft, but until Wednesday the government denied using such tactics.
A report by the state-run Myanmar News Agency on Wednesday, which was published on Thursday in the state newspaper, New Light of Myanmar, said the military used aircraft to clear rebels from a hilltop not far from the Chinese border.
"Air cover was used in the attack," the report said. "Weapons and ammunition were seized."
The Myanmar Army's goal was to keep supply lines open, the report said, adding that the army "did not launch offensives."
Fighting between government troops and the Kachin Independence Army has tarnished the reform efforts of President Thein Sein, who is leading the country's transition from a military dictatorship to a democracy.
The Kachin, like Myanmar's other ethnic minorities, have long sought greater autonomy from the central government. They are the only major ethnic rebel group that has not reached a cease-fire agreement with Mr. Thein Sein's government, which came to power in March 2011 after almost five decades of military rule.
His government has been praised for instituting changes that include liberalizing the economy, abolishing most media censorship and opening the once-isolated country to foreign investment. He has also led reconciliation efforts with the political opposition, led by Daw Aung San Suu Kyi, the country's leading democracy advocate.
But friction with ethnic minorities is seen as a danger to the fledgling democracy.
Although Mr. Thein Sein is a former general himself, his public appeals for an end to the army's offensive in the borderland areas have gone unheeded, leading diplomats to voice concerns about a possible rift between the military and his civilian government. Peace talks between government negotiators and the rebels have foundered.
The military's objective appears to be the capture of the rebel base at Laiza, a town on the border with China. Tens of thousands of refugees have fled the fighting, some to China. The current round of fighting began in June 2011 when a 17-year cease-fire ended.
Capturing the rebel base at Laiza would be a victory for the military of Myanmar, formerly Burma, but it is unlikely that it would stop the fighting. The Kachin specialize in guerrilla tactics honed over decades: their warriors were allies of British and American troops against Japanese soldiers during World War II.
Myanmar's state news media have given few details about the fighting and until now rarely offered casualty tallies. The Myanmar News Agency's report listed a series of clashes in which "soldiers were injured and lost their lives."
A State Department spokeswoman, Victoria Nuland, called the use of air power "extremely troubling."
At a briefing in Washington on Wednesday Ms. Nuland said, "We are continuing to urge the government of Burma and the Kachin Independence Organization to cease this conflict."
This article originally appeared in The New York Times.