The United Nations' envoy for Myanmar on Sunday strongly condemned continuing bloodshed after at least 18 protesters were killed in one of the deadliest days since the country's February 1 coup.

"The international community, including regional actors, must come together in solidarity with the people of Myanmar and their democratic aspirations," Christine Schraner Burgener said in a statement.

She said the Myanmar military was defying international calls for restraint, adding she had heard "heartbreaking accounts of killings, mistreatment of demonstrators and torture of prisoners" from contacts inside the Southeast Asian country.

"The ongoing brutality, including against medical personnel and destruction of public infrastructure, severely undermines any prospects for peace and stability," she said.

Myanmar's junta late Sunday imposed martial law in two densely populated Yangon townships.

More than 80 people have been killed in mass protests since the military wrenched civilian leader Aung San Suu Kyi from power -- a toll expected to rise dramatically after Sunday's violence.

© AFP