Ethnic Kachin rebels in Myanmar have accused government troops of launching two artillery attacks against the city that serves as their headquarters.
No casualties or significant damage were reported as a result of the alleged strikes on Sunday.
Army forces based at a nearby outpost fired at least seven 105mm shells at the northern city of Laiza, four rounds in the morning and three more before dusk, rebel spokesman La Nan told The Associated Press.
A senior government official, speaking on condition of anonymity, denied the claim.
Al Jazeera's Wayne Hay, reporting from Bangkok in neighbouring Thailand, said a representative from the Kachin Independent Army (KIA) told him that two jets had fired on the area.
"He said that those two jets had attacked a KIA outpost about 10km from the town of Laiza, which is where the KIA is headquartered," he said, adding that the area is similar to one attacked by Myanmar helicopters and fighter jets last week.
Our correspondent said that "using air power against the rebels in Kachin state is certainly an escalation in what has been a very long-running war."
Fighting has wracked northern Myanmar since a ceasefire that held for nearly two decades broke down in June 2011 after rebels refused to abandon a strategic base near a hydropower plant that is a joint venture with a Chinese company.
The conflict has forced around 100,000 Kachin from their homes since then, and many are in camps near Laiza, which is held by the rebels and located near the Chinese border.
Fighting between the two sides appears to have intensified in recent weeks, with the government pounding rebel positions with helicopter gunships and fighter jets.
La Nan, a spokesman for the Kachin Independence Army, said it was the second artillery attack on Laiza since December 19.
Another rebel official, who declined to be identified because he is not a spokesman for the fighters, said the shells fired Sunday morning fell near several homes that were hit by shrapnel but not significantly damaged.
Rebel forces did not return fire, he said.
Tension with ethnic minorities fighting for greater autonomy in Myanmar is considered one of the biggest major long-term challenges for reformist President Thein Sein, who inherited power in 2011 from the army, which ruled for almost half a century.
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 truce with Thein Sein's administration.
The recent fighting in Kachin state escalated on Christmas Day, when the rebels rejected a government demand that supply convoys be allowed to reach an army base, contending that they carried ammunition that could be used to attack their nearby headquarters.
The government then used fighter planes and helicopters to mount attacks and seized one of the guerrillas' hilltop outposts.
The army says it has launched recent air attacks to clear a road of rebels so it could supply a base.
On Friday, the government said in a statement that the army had been given orders to cease all offensives against the guerrillas, but that it had to protect its soldiers after the Kachin continued to set off land mines and ambush their forces.
Source: Al Jazeera and agencies