UN human rights investigators 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 Mr Darusman, who is leading an investigation that Myanmar has vowed to reject.
"We will go where the evidence leads us," he said.
Myanmar's ambassador Htin Lynn said Mr Darusman's investigation was "not a helpful course of action" and said Myanmar was taking proportionate security measures against terrorists, and was making efforts to restore peace.
Myanmar leader Aung San Suu Kyi has condemned all human rights violations and said anyone responsible for abuses in Rakhine State would face the law, and she felt deeply for the suffering of everyone caught up in conflict there.
She said Myanmar did not fear international scrutiny and was committed to a sustainable solution to the conflict.
It was her first address to the nation since attacks by Rohingya Muslim insurgents on 25 August sparked a military response that has forced more than 410,000 Rohingya into Bangladesh.
The United Nations has branded the military operation as ethnic cleansing.
Ms Suu Kyi did not address that accusation but said her government condemned rights violations and anyone responsible for abuses would face the law.
We condemn all human rights violations and unlawful violence. We are committed to the restoration of peace and stability and rule of law throughout the state
Special report: Crisis in Myanmar
Long feted in the West for her role as champion of Myanmar’s democratic opposition in the Buddhist-majority country during years of military rule and house arrest, Ms Suu Kyi has faced growing criticism for saying little about the abuses faced by the Rohingya.
"Human rights violations and all other acts that impair stability and harmony and undermine the rule of law will be addressed in accordance with strict laws and justice," she said.
"We feel deeply for the suffering of all the people caught up in the conflict."
The United States urged the Myanmar government yesterday to end military operations in Rakhine state, grant humanitarian access, and commit to aiding the safe return of civilians to their homes.
Myanmar's powerful military remains in full charge of security and Ms Suu Kyi did not comment on the military operations except to say that since 5 September, there had been "no armed clashes and there have been no clearance operations".
"Nevertheless, we are concerned to hear that numbers of Muslims are fleeing across the border to Bangladesh," she said.
"We want to find out why this exodus is happening. We would like to talk to those who have fled as well as those who have stayed. I think it is very little known a great majority of Muslims in the Rakhine state have not joined the exodus."
She said her government had been making every effort to restore peace and stability and to promote harmony between the Muslim and largely Buddhist Rakhine communities.
Ms Suu Kyi is banned from the presidency by the military-drafted constitution because her children have British citizenship.
She holds offices of the state counsellor and minister for foreign affairs, and is the de facto leader of the administration.
In her address, Ms Suu Kyi did not use the term Rohingya to refer to the Muslim minority in Rakhine State.
Members of the 1.1 million group, who identify themselves by the term Rohingya, are seen by many Myanmar Buddhists as illegal immigrants from Bangladesh. The term is a divisive issue.
Most Rohingya do not have Myanmar citizenship.
