The Geneva-based human rights council voted in March to create a Myanmar fact-finding mission, in a politically sensitive move that faced fierce resistance from the civilian-led government of Aung San Suu Kyi.
The mission was ordered to "urgently" investigate abuses reportedly committed by the security forces, particularly in Rakhine state where troops have been accused of raping, torturing and murdering members of the Rohingya community.
Decorated Indian lawyer and women's rights campaigner, Indira Jaising, Sri Lanka's former human rights chief Radhika Coomaraswamy and Christopher Dominic Sidoti, a prominent human rights advocate from Australia, were appointed to lead the probe.
But it is not yet clear if they will be granted access to Rakhine, or even be permitted to land in Myanmar.
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Speaking in Brussels earlier this month, Suu Kyi made clear that her government had "disassociated" itself from the resolution setting up the probe, calling it out of touch "with what is actually happening on the ground."
The north of Rakhine state has been under lockdown since October, when the military launched a campaign to hunt down Rohingya militants who staged deadly attacks on police posts.
An earlier UN rights office report based on testimony from Rohingya refugees in Bangladesh said Myanmar's security forces may be guilty of crimes against humanity.
Myanmar has rebuffed those charges and has refused to allow international observers into the area.
The rights council called on the government to give investigators "full, unrestricted and unmonitored access to all areas".
Matthew Smith, who heads the Fortify Rights watchdog in Bangkok which closely tracks the Rakhine situation, told AFP the government had "no defensible reason to not cooperate with this mission."
The mission is scheduled to give the rights council an oral update of their findings in September.