Tom Andrews, the United Nations special rapporteur on human rights in Myanmar, called for an emergency summit to sharpen the response and said it should include the southeast Asian country's neighbours and global powers.

Myanmar's military has unleashed a deadly wave of violence as it struggles to quell nationwide protests against the February 1 ousting of the civilian government and arrest of leaders including Aung San Suu Kyi.

"Conditions in Myanmar are deteriorating but they will likely get much worse without an immediate, robust, international response in support of those under siege," Andrews said in a statement.

"The limited sanctions imposed by member states do not cut the junta's access to revenue that help sustain its illegal activities, and the slow pace of diplomacy is out of step with the scale of the crisis.

"The incremental approach to sanctions has left the most lucrative business assets of the junta unscathed. It needs to be replaced by robust action that includes a diplomatic offensive designed to meet the moment."

Andrews, who does not speak for the UN but is mandated to report his findings to the global body, called for the emergency summit to involve among others the Committee for Representing Pyidaungsu Hluttaw (CRPH) -- a group of ousted parliamentarians working underground against the junta.

Without a focused diplomatic solution, he said he feared the situation would further deteriorate with more murders, enforced disappearances and torture.

A combination of domestic peaceful resistance, sustained pressure and international diplomatic momentum would save lives and have a far greater chance of success than taking up arms, the American said.

"I fear that the international community has only a short time remaining to act," Andrews said.

Security forces opened fire on Thursday on anti-coup protesters in the eastern Karen state in the latest flare-up, as demonstrators took to the streets in nationwide dawn rallies.

Protesters have continued calling for the military to step down, defying night-time curfews to stage candlelit vigils for the dead, and taking to the streets early in dawn marches to avoid security forces.