UN rights experts have warned that the violence against women and children in Rakhine State "may amount to crimes against humanity".

The UN Committee on the Elimination of Discrimination against Women (CEDAW) and the Committee on the Rights of a Child called on Myanmar authorities to "promptly and effectively investigate and vigorously prosecute cases of violence against women and children" in northern Rakhine.

"We are particularly worried about the fate of Rohingya women and children subject to serious violations of their human rights, including killings, rape and forced displacement," the committees said in a statement on Wednesday.

READ MORE: Who are the Rohingya?

"Such violations may amount to crimes against humanity and we are deeply concerned at the state's failure to put an end to these shocking human rights violations being committed at the behest of the military and other security forces, and of which women and children continue to bear the brunt."

More than 507,000 Rohingya have fled to Bangladesh since Myanmar's army launched a military crackdown in response to an attack by Rohingya fighters on dozens of police posts and an army base on August 25.

Rohingya who have fled have told stories of rape and other sexual abuse, indiscriminate killings and arson by Myanmar security forces.

The UN has previously called the Rohingya exodus from Myanmar to Bangladesh "the most urgent refugee crisis in the world".

The mainly Muslim minority, who live primarily in Rakhine State, is not recognised as an ethnic group in Myanmar, despite having lived there for generations. They have been denied citizenship and are stateless.

On Monday, Bangladesh's foreign minister said Myanmar proposed taking back Rohingya refugees who had fled to his country.

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Speaking to reporters after a meeting with Myanmar official Kyaw Tint Swe, Bangladesh Foreign Minister AH Mahmood Ali said both countries agreed to form a joint working group to begin work on the massive repatriation.

No details were provided about how such repatriation will take place and rights groups fear the hundreds of thousands of Rohingya without documents will be left in limbo.

The two UN rights committees on Wednesday pointed to how the statelessness of Rohingya women and children and "their protracted displacement had exposed them to high levels of poverty and malnutrition".

"We urged the Myanmar authorities to address the needs of internally displace Rohingya women and children, as well as Rohingya refugee women and children living in camps in neighbouring countries, with the support of the international community," the committees said.