Acute shortages of water and medical treatment in western Myanmar following attacks on humanitarian groups are the latest hardships imposed on Rohingya Muslims that "could amount to crimes against humanity", a U.N. expert said Monday.

The United Nations' human rights envoy to the country, Tomas Ojea Quintana, said a wave of attacks against aid organizations had choked off health, water and food supplies, increasing the vulnerability of the Rohingyas.

Dozens of activists took to the streets of Myanmar's main city Yangon Friday for a rare campaign against anti-hate speech in a country wracked by sectarian violence and rising Buddhist nationalism.

Volunteers urged passers-by to focus on promoting social harmony in the former junta-ruled nation, where scores have been killed and tens of thousands left homeless in anti-Muslim unrest since 2012.

The U.N. agency tasked with facilitating Myanmar's first census in decades on Tuesday said it was "deeply concerned" over a government decision to bar Muslims from identifying as Rohingya, warning it could stoke tensions.

Myanmar had said it would conduct the rare survey in accordance with international standards and "explicitly agreed" to allow people to be able to choose their own ethnicity, the United Nations Population Fund (UNFPA) said in a statement.

Thousands of vulnerable people in strife-torn western Myanmar are close to running out of food and clean water, according to aid groups forced to flee the region after a wave of mob violence.

Many displaced people -- mostly stateless Rohingya Muslims -- living in bleak camps in Rakhine State are completely reliant on humanitarian deliveries, which have now stopped as a result of the unprecedented attacks on relief organisations.

Two detainees at an immigration center in Japan died over the weekend, an official said Monday, just months after the death of another man at the same facility.

An Iranian man in his 30s choked on his dinner on Friday, a spokeswoman at the immigration center in Ushiku, northeast of Tokyo, told Agence France Presse, adding that he was taken to hospital but died on Saturday afternoon.

Tens of thousands of census-takers fanned out across Myanmar on Sunday to gather data for a rare snapshot of the former junta-ruled nation that is already stoking sectarian tensions.

Groups of school teachers and local officials began the 12-day population survey -- the first since 1983 -- traveling from house to house in an ambitious drive aimed at counting everyone across the poverty-stricken nation.

Myanmar said Saturday that Muslims would not be allowed to register as "Rohingya" in its first census in three decades despite U.N. assurances, on the eve of a survey that has fanned sectarian tensions.

The move came as Buddhists in an unrest-hit western state vowed to boycott the census over fears it could lead to official recognition for the Rohingya, viewed by the United Nations as among the world's most persecuted minorities.

An 11-year-old girl was accidentally killed when Myanmar security forces fired warning shots to disperse mobs targeting international aid groups in a strife-hit western state, police said Friday.

The girl was shot Thursday at her home near a U.N. World Food Program warehouse in the Rakhine state capital Sittwe that was targeted by rioters, Lieutenant Colonel Min Aung told Agence France Presse.

Dozens of aid workers were under police protection in western Myanmar Thursday sparking U.N. and U.S. alarm after mobs attacked the offices of international relief agencies in a new surge of violence.

Authorities tightened a curfew in Sittwe, the capital of volatile Rakhine State, after gangs of Buddhists ransacked the offices of aid groups who have faced accusations of bias in favor of local Muslims.

Several foreign aid workers were under police protection Thursday in unrest-torn western Myanmar, authorities said, after security forces fired warning shots to disperse a mob laying siege to the offices of an international humanitarian group.

Hundreds of local Buddhists massed around the offices of Germany-based medical aid group Malteser International late Wednesday in Sittwe, the capital of volatile Rakhine State, hurling stones and prompting police to escort at least eight staff to safety.