A top aide to United Nations Secretary-General Ban Ki-moon visited Burma's western Rakhine state Wednesday, as security forces there grappled with sectarian violence between Buddhists and Muslims that has left at least 21 people dead.

U.N. officials told VOA that Vijay Nambiar, the U.N.'s top envoy to Burma, traveled to Rakhine accompanied by Burma's Border Affairs Minister Thein Htay and 10 Muslim leaders from Rangoon. Nambiar visited the city of Maungdaw and the state capital, Sittwe, where he discussed the situation with state officials.

The visit came after Bangladesh denied the U.N. High Commissioner for Refugees' request that it open its borders to Rohingya people fleeing the fighting. Bangladesh's Foreign Ministry said it is not in the country's best interest to allow the Rohingyas in.

Violence erupted June 3 when a mob of Buddhists in Rakhine ambushed a bus and killed 10 Rohingya Muslim passengers, in apparent retaliation for the earlier rape and murder of a Buddhist woman by three Muslims.

President Thein Sein has declared a state of emergency and sent army troops into Rakhine, where a curfew is in place. In addition to the killings, the area has seen a wave of rioting and arson that has destroyed hundreds of homes.

Activists reported that the situation calmed on Wednesday with the presence of the army and dusk-to-dawn curfews imposed on many parts of the region.

But Chris Lewa of the Arakan Project, which monitors western Burma, tells VOA there is now concern that Burmese security forces may be making arbitrary arrests, particularly in the border city of Maungdaw.

“In Maungdaw, the situation has calmed down a little bit last night with the presence of the army. But there are still a number of incidents that have taken place in different parts of the township, especially around the city. But we see now it's mostly people being arrested. And nobody knows what is going to happen to them or for what reason they have been arrested.”

Lewa said the Burmese government must work to repeal laws that deny citizenship for Rohingya Muslims in order to ensure national reconciliation.

Burma does not classify its estimated 800,000 Rohingyas as Burmese citizens, instead regarding them as illegal immigrants from neighboring Bangladesh. For its part, Bangladesh denies both immigration rights and formal refugee status to the several hundred thousand Rohingyas living in refugee camps there.

President Thein Sein has warned recently that the violence could jeopardize Burma's nascent reform process. He said the unrest is fueled by “hatred and revenge based on religion and nationality” and noted it could spread to other parts of the country. If that happens, he said the country's stability, peace, and democratization process could be severely affected.