The US embassy in Yangon said it was "deeply concerned" over clashes involving ethnic armed groups and the military in northern Myanmar that have displaced thousands of people, warning that the violence threatened to unravel the country's delicate peace process.
Heavy bouts of fighting broke out last week in Shan state between two ethnic rebel groups in the region, the Restoration Council for Shan State (RCSS) and the Ta'ang National Liberation Army (TNLA).
The flare-up of violence comes during a complicated political transition from an army-backed government to Aung San Suu Kyi's pro-democracy party, which dominated historic polls last year.
"The US embassy is deeply concerned about ongoing clashes in Shan State involving the Ta'ang National Liberation Army (TNLA), the Restoration Council of Shan State (RCSS), and the military," the embassy said in a statement published Friday evening.
"We urge all sides to exercise restraint and recommit to dialogue so that the peace process may remain on track, and those displaced can return to their homes and resume their lives," it said.
Since the beginning of the month at least 4,300 people have fled their homes seeking refuge from the violence, according to estimates from the United Nations' country Office for the Coordination of Humanitarian Affairs.
The conflict has exploded in townships in the north of Shan state -- a region home to the Palaung ethnic group, whose interests the TNLA says it represents.
The RCSS has previously been based further south.
The TNLA has accused the Myanmar army of assisting the RCSS, which is one of eight groups that participated in government-led peace talks seeking to end decades of civil warfare between the state and the country's patchwork of ethnic minorities.
But the TNLA and other major ethnic militias locked in ongoing conflicts with the military boycotted the dialogue, which was steered by the outgoing quasi-civilian government that took power in 2011 and transitioned Myanmar out of decades of military junta rule.
It is unclear what sparked the recent clashes in Shan state, but the lack of full participation in the peace deal has raised concerns that rebel groups could begin vying with each other to control territory.
Efforts to achieve a nationwide truce will now fall to Suu Kyi's National League for Democracy, which is set to form a government in April.
Ahead of November's elections, analysts predicted that Suu Kyi, 70, would struggle to win support among minority voters because of her ethnic Bamar heritage.
But her party scooped a vast majority of elected seats across the country, even beating out some ethnic parties on their home turf in the frontier regions.
The democracy champion has since vowed to make ethnic affairs a priority of her administration.