Bangkok: Soldiers from Myanmar used acid to burn away the faces of slaughtered Rohingya Muslims so they couldn’t be identified before the bodies were thrown into mass graves, shocking new evidence has revealed.

Time-stamped cell phone videos obtained by Associated Press of the graves show blue-green puddles of acid sludge surrounding corpses, jutting into the air and missing both heads and torsos.

Interviews with survivors who have reached Bangladesh confirm at least five previously unreported mass graves and details of a massacre in Gu Dar Pyin village in Buthidaung township.

Villagers said they saw soldiers buying 12 containers of acid two days before the massacre, indicating that an attempt to cover it up was pre-planned.

The US State Department said it was “deeply, deeply troubled” by the new evidence and called for Myanmar’s government to allow an independent investigation.

Yanghee Lee, the United Nations’ special envoy on human rights in Myanmar, said mounting evidence of atrocities in Rakhine bear “the hallmarks of genocide."

Ms Lee reiterated calls for those responsible for the slaughter to be brought to justice.

“No stones must be left unturned because the people, the victims, the families of the victims definitely deserve an answer,” she said, wrapping up a mission that took her to squalid camps accommodating almost one million Rohingya refugees in Bangladesh.

In a scathing assessment of Myanmar's government Ms Lee said it has “failed to usher in a new eras of openness and transparency and is instead persisting with repressive practices of the past.”

Myanmar’s military has acknowledged the existence of only one mass grave in Rakhine and the government led by Nobel laureate Aung San Suu Kyi denies any mass killings, rapes and burnings, even though they have been documented in extensive testimonies gathered by the UN, human rights groups and media outlets including Fairfax Media.

Doctors Without Borders says surveys in Rohingya camps indicate as many as 13,000 people have been killed in Rakhine since August, many of them children.

Phil Robertson, deputy Asia director at Human Rights Watch, said the identification of new graves “raises the stakes for the international community to demand accountability from Myanmar,” and called on the US and other nations to impose sanctions on military commanders responsible for the killings.

The Turnbull government has described reports of violence in Rakhine as disturbing but has refused to condemn Suu Kyi’s government or the military.

The Australian Defence Force continues to provide training and other support to the military.

Associated Press said interviews with survivors of Gu Dar Pyin suggests up to 400 villagers were slaughtered in an attack by soldiers and Buddhist mobs on August 27, and that many more graves hold more people.

Soldiers wielded rifles, knives, rocket launchers and grenades as well shovels to dig graves and acid to burn away faces, according to the survivors.

Buddhist villagers then moved through in a mopping up operation, using knives to cut the throats of the injured, survivors said.

More than 688,000 Rohingya have fled their homelands in Rakhine since August, creating a humanitarian emergency in the Bangladesh camps.

Rohingya are called Bangladeshi interlopers and denied citizenship and other basic rights in Buddhist-majority Myanmar, the country also called Burma, despite they have lived there for centuries.