UN human rights investigators on Tuesday said they needed "full and unfettered" access to Myanmar to probe a grave and ongoing crisis, urging the government to rethink its rejection of the probe.

"It is important for us to see with our own eyes the sites of these alleged violations", the head of UN-backed fact-finding mission, Marzuki Darusman, told the Human Rights Council, asking for "full and unfettered access to the country."

"There is a grave humanitarian crisis underway that requires urgent attention," added Darusman, who is leading an investigation that Myanmar has vowed to reject.