Forces of the Kachin Independence Army (KIA), one of the ethnic factions opposed to Myanmar's coup, attacked military positions at the northwestern jade mining town of Hkamti on Saturday, local media reported.
The attack marks an advance into new territory by the KIA at a time Myanmar has been plunged into chaos since the army seized power on Feb. 1, detained elected leader Aung San Suu Kyi and cut short a decade of democratic reforms.
KIA fighters attacked an army post at Hkamti township in the Sagaing region early on Saturday, the Irrawaddy and Mizzima online publications said. Pictures showed columns of dark smoke rising from what they said was the scene of the attack.
KIA spokesman Naw Bu told Reuters he was aware of the attack but could give no details. Reuters was unable to reach a junta spokesman for comment on the reports.
"The fighting is still ongoing. I can still hear the gunshots," Mizzima quoted one resident as saying.
It said the site attacked was near a mining venture that involves the military-owned Myanma Economic Holdings Ltd. conglomerate.
Reuters was unable to confirm the reports independently.
Since the coup, open conflict resumed between the army and the KIA, which has been fighting for greater autonomy for the Kachin people for some six decades and has voiced support for anti-junta protesters.
Mizzima said the army was using jets in attacks on the KIA at Hkamti, a town on the Chindwin river in a remote region rich in jade and gold that lies about 50 km (30 miles) from the border with India.
The army has carried out numerous bombing attacks on KIA positions in recent weeks and has also clashed with ethnic armies in the east and west of Myanmar.
Security forces have killed at least 812 people since the coup, according to the Assistance Association for Political Prisoners activist group. The military disputes this figure and says at least two dozen members of the security forces have also been killed.
The army seized power alleging fraud in a November election won by Suu Kyi's National League for Democracy. The then electoral commission had rejected its accusations. On Friday, local media quoted an official of the new electoral commission appointed by the junta as saying there was a plan to dissolve the NLD.