The United Nations (UN) began work on Wednesday inside Myanmar's violence-torn northern Rakhine state, the first time its agencies have been granted permission to operate there since more than 700,000 Rohingya Muslims fled the area last year.

The UN has been waiting for access to the epicentre of the military's "clearance operations" against the Rohingya minority since June when its refugee and development agencies signed a deal with the government.

Its work is highly sensitive inside Rakhine, a state cut deep with ethnic and religious hatred and where Buddhist locals stand accused of helping the army chase out their Muslim neighbours.

Many Rakhine accuse international aid groups, including the UN, of a pro-Rohingya bias and foreign aid groups have been granted very limited access to the state.

The task is complicated further as the UN's rights arm is expected to heavily censure Myanmar again in the coming days when it publishes in full the findings of its investigation into atrocities against the Rohingya.

On Friday, specialists from the UNHCR and UNDP agencies were finally given permission to enter northern Rakhine before work began on Wednesday to assess local conditions.

"The team is on the ground and commenced with the first assessments today," UNHCR Spokeswoman Aoife McDonnell told AFP.

This first step of the UN's "confidence-building measures" is expected to take two weeks and will cover 23 villages and three additional clusters of hamlets.

It was not immediately clear which villages they will visit or which communities the UN teams will consult.

The expectation is this "very initial and small step in terms of access will be expanded rapidly to all areas covered" by the agreement, McDonnell said.

Lockdown

The stateless Rohingya are widely seen as illegal immigrants by Myanmar's majority-Buddhist population, complicating the repatriation of those who fled to Bangladesh.

Last August's crackdown by Myanmar's army pushed hundreds of thousands of Rohingya across the border. Refugees have carried accounts of rape, murder, arson and torture perpetrated by the military and buttressed by Rakhine mobs.

The northern part of Rakhine has been locked down since then, with journalists and observers only allowed to visit on short, chaperoned trips.

The deployment of the two UN agencies comes as Myanmar faces growing demands for accountability over its treatment of the Rohingya.

A UN-led report last week two weeks ago called for the prosecution of army chief Senior General Min Aung Hlaing and five other top-ranking generals for genocide, war crimes and crimes against humanity.

That was swiftly followed by a ruling by the International Criminal Court (ICC) that it has jurisdiction to open a probe into "deportations" of the Rohingya, saying it was a cross-border crime.

Myanmar is not a signatory of the statute underpinning the tribunal and has rejected the remit of the court. The move could potentially lead to a wider probe and an eventual trial.

Myanmar will once again be under scrutiny at the UN General Assembly in early October, though civilian leader Aung San Suu Kyi will be notably absent.

Once considered a pro-democracy and human rights icon, Suu Kyi's reputation globally is in tatters for failing to stand up for the Muslim minority.

Myanmar has vehemently denied nearly all allegations of atrocities, justifying its actions as legitimate means to root out Rohingya militants.