Tomas Ojea Quintana, the UN's special rapporteur on human rights in Myanmar, urged the country's reformist government to tackle the root cause of discrimination against Muslim Rohingya living in the strife-hit region.
"The underlying tensions that stem from discrimination against ethnic and religious minorities pose a threat to Myanmar's democratic transition and stability.
"I urge all sides to exercise restraint, respect the law and refrain from violence," he said in a statement released late Wednesday in Geneva.
President Thein Sein, a former general credited for a string of political reforms since taking power last year, has imposed a state of emergency in Rakhine state where clashes between Buddhists and Rohingya have caused dozens of deaths and forced hundreds of people from both sides to flee their homes.
"The latest death toll we can confirm is 28 with 53 people wounded," a government official, who did not want to be named, told AFP in the state capital Sittwe, without saying whether they were Buddhist or Muslim Rohingya.
Previously the official toll stood at 25 dead since Friday, although Rohingya leaders say the real toll is much higher.
The figure does not include 10 Muslims who were killed on June 3 by a Buddhist mob in apparent revenge for the rape and murder of a woman, which sparked the violence in Rakhine.
In recent days local residents have been seen on the streets wielding knives, swords and sticks, while hundreds of homes have been burned down.
The Buddhists and Rohingya have both accused each other of violent attacks.
An uneasy calm has now returned to central Sittwe which is under a dusk-to-dawn curfew. But evidence of the violence lingers: a decomposing body was seen in a sewage drain in the city.
More than 30 people were held after breaking the curfew on Wednesday night, the official added.
Hundreds of Rohingya, many of them women and children, have attempted to flee to neighbouring Bangladesh in rickety boats in recent days, but have been turned away.
The United States on Wednesday urged Dhaka to respect its international obligations under the relevant refugee conventions and not to turn away Rohingya fleeing the violence.
"We are concerned that Bangladeshi authorities appear to have intercepted and turned back persons fleeing the ethnic and religious violence in Burma," State Department spokeswoman Victoria Nuland said, using Myanmar's former name.
Decades of discrimination have left the Muslim Rohingya stateless and viewed by the United Nations as among the most persecuted minorities on the planet.
About 800,000 Rohingya live in Myanmar, according to the UN, mostly in Rakhine.
The Myanmar government considers the Rohingya to be foreigners, while many citizens see them as illegal immigrants from Bangladesh and view them with hostility.
Rohingya are subject to forced labour, restrictions on freedom of movement, lack of land rights, education and public services, according to a UN refugee agency (UNHCR) report published in December.
The UN has evacuated most of its foreign staff from its main base in Rakhine.
But Vijay Nambiar, UN chief Ban Ki-moon's special adviser on Myanmar, flew into Rakhine on Wednesday to see the situation.