UN body will collect, consolidate, preserve, and analyse evidence of the most serious international crimes.
The UN Human Rights Council voted to set up a body to prepare evidence of human rights abuses in Myanmar - including possible genocide against the Muslim Rohingya - for any future prosecution.
The 47-member council voted by 35 votes to three, with seven abstentions, on Thursday in favour of a resolution brought by the European Union and the Organization of Islamic Cooperation.
China, the Philippines, and Burundi voted against the move.
A year ago, Myanmar troops led a brutal crackdown in Rakhine state in response to attacks by the Arakan Rohingya Salvation Army on 30 Myanmar police posts and a military base.
More than 700,000 Rohingya fled the crackdown and most are now living in refugee camps in neighbouring Bangladesh.
The resolution sets up a body to "collect, consolidate, preserve and analyse evidence of the most serious international crimes and violations of international law committed in Myanmar since 2011, and to prepare files in order to facilitate and expedite fair and independent criminal proceedings".
WATCH: 'Genocidal intent': UN says Myanmar military leaders must face prosecution (3:05)
The new agency is to work closely with any future prosecution brought by the International Criminal Court, which said earlier this month that it had jurisdiction over deportations of Rohingya from Myanmar to Bangladesh.
Myanmar Ambassador Kyaw Moe Tun said the resolution was based on the report of a UN fact-finding mission that his government had categorically rejected, and which was unbalanced, one-sided and encouraged disunity of the country.
"The draft resolution is based on serious but unverified accusations and recommendations … that could even endanger the national unity of the country," he said.
Kyaw Moe said the resolution's intrusive language and demands would not contribute to finding lasting resolutions to the delicate situation in Rakhine state.
The UN report said Myanmar's military carried out mass killings and gang rapes of Rohingya with "genocidal intent" and called for commander-in-chief Min Aung Hlaing and five named generals to be prosecuted for the gravest crimes.
In Thursday's resolution, the council said there was enough information to warrant a competent court "to determine their liability for genocide".
Chinese diplomat Chen Cheng told the council that Beijing opposed the resolution because it was very likely to exacerbate the tensions. "This is in no one's interest," he said.
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