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 prioritize the safety and well-being 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 Feb. 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.
But it remains to be seen to what extent the NUG can influence the course of events.
"The NUG declaration has received strong support on Myanmar social media," said Richard Horsey, a Myanmar expert at the International Crisis Group.
But he 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.
'BACK TO THE DRAWING BOARD'
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".
While Western countries have imposed sanctions to press the junta, 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," Malaysian foreign minister Saifuddin Abdullah, referring to a plan the block put forward to the junta in April to end the violence, told an online news conference.
But 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.
But no side in the conflict has confirmed this.
In Washington, a U.S. 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 U.S.-funded RFA (Radio Free Asia) reported.
"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.
As opposed to most Western countries that have condemned the army for ousting Suu Kyi's government, China which has considerable economic interests in Myanmar has taken a softer line and said its priorities are stability and not interfering in its neighbour.
China's state-run Global Times newspaper warned that if Western countries backed anti-junta forces militarily it may trigger violent turmoil.
"If armed clashes are indulged and political extremist action is encouraged, then the country will be plagued by endless battles and trouble," it said in an opinion piece.
(Reporting by Reuters Staff Writing by Ed Davies Editing by Robert Birsel) ((Ed.Davies@thomsonreuters.com;))