UN Secretary General Ban Ki-moon on Monday called for an end to the bloodshed in war-torn northern Myanmar that has marred the new regime's reformist image.
Continued heavy fighting in Kachin State, in the far north of the country, "is inconsistent with the successful conclusion of the ceasefire agreements with all other major groups", Ban told lawmakers in a landmark address to parliament.
"The Kachin people should no longer be denied the opportunity that a ceasefire and a political agreement can bring for peace and development," he added.
Myanmar's new quasi-civilian government has inked a series of ceasefires with several disparate ethnic rebel groups as part of a range of reforms since it came to power last year.
But violence in Kachin has continued to rage since a 17-year ceasefire was shattered last year.
Tens of thousands of people have been displaced by clashes between government troops and guerrillas with the Kachin Independence Army (KIA).
Although the UN recently managed to send aid convoys into hard-to-reach parts of Kachin, many refugees remain in dire need of assistance and with the monsoon looming, conditions are expected to become even more desperate.
"Let me acknowledge the humanitarian access that now we have in Kachin. That access must continue," Ban told legislators.
Civil war has gripped parts of Myanmar since independence in 1948. An end to the conflicts and alleged rights abuses involving government troops is a key demand of the international community.
Myanmar official media has made rare acknowledgements of the unrest in Kachin in recent days, accusing the rebels of a series of attacks.
On Monday state mouthpiece New Light of Myanmar accused the rebels of firing heavy weapons into a village, killing a five-year-old child and injuring two as well as planting a mine that derailed a passenger train, wounding two men.
On Sunday the newspaper reported that KIA rebels had killed four officials in an assault on a government office in Waingmaw Township, that had also left three people missing.
In a separate incident involving heavy weapons fire in another area, 200 KIA fighters were said to have captured vehicles belonging to a Myanmar construction giant linked to a Chinese company working at one of the dam sites.
The army was "in hot pursuit", the report added.