Southeast Asian and Western countries have urged all sides in Myanmar to refrain from violence and allow in aid, after a shadow government, formed by opponents of military rule, declared a nationwide uprising against the junta.
The National Unity Government (NUG) said on Tuesday it was launching a "people's defensive war", signalling what appeared to be a bid to coordinate groups fighting the military as well as calls for troops and officials to switch sides.
A military spokesman dismissed the call for revolt as a ploy to gain world attention and said it would not succeed.
There were no immediate reports of violence on Wednesday, though security forces were out in strength in Myanmar's biggest city, Yangon. A day earlier, there were protests and a flare-up in fighting between the army and ethnic minority insurgents.
"All parties must prioritise the safety and wellbeing of the Myanmar people," Indonesian foreign ministry spokesman Teuku Faizasyah told Reuters, noting humanitarian assistance could only be distributed if the situation on the ground was secure.
Indonesia has taken the lead among Myanmar's neighbours in trying to resolve a crisis triggered when the military toppled the elected government of Aung San Suu Kyi on February. 1.
The security forces have killed hundreds of protesting democracy supporters and some opponents of military rule have formed armed groups under the banner of People's Defence Forces.
They have also forged alliances with ethnic minority groups fighting for self-determination who have long seen Myanmar's army as their enemy.
Richard Horsey, a Myanmar expert at the International Crisis Group, said it was not clear if opposition forces had the capacity to escalate the fight against Myanmar's well-equipped military and the NUG's declaration of "war" might backfire by making it harder for some countries to support it.
Britain's Ambassador to Myanmar Pete Vowles said in a post on Facebook "we strongly condemn the junta's coup and brutality" and urge "all sides to engage in dialogue".
The Association of Southeast Asian Nations has been leading efforts for a diplomatic solution, but some members of the bloc have become exasperated by the lack of progress.
"I can only say that we are frustrated that the five-point consensus could not be implemented as quickly as possible," said Malaysian foreign minister Saifuddin Abdullah, referring to a plan the block put forward to the junta in April to end the violence.
Referring to the NUG's call for a revolt, he said: "Now with the latest event, you really have to go back to the drawing board."
An ASEAN envoy to Myanmar was quoted as saying on the weekend that the military had accepted his proposal for a ceasefire until the end of the year to ensure distribution of humanitarian aid.
In Washington, a US State Department spokesperson noted the declaration of a "people's defensive war" but called for peace to allow the delivery of aid and medicine.
"The United States does not condone violence as a solution to the current crisis ... and calls on all sides to remain peaceful," said the spokesman.