"The recent episode of violence in Meiktila in central Myanmar raises concerns that sectarian violence is spreading to other parts of the country," U.N. Special Adviser on the Prevention of Genocide Adama Dieng said.
Myanmar President Thein Sein imposed martial law over parts of Myanmar last week following clashes between Muslims and Buddhists. Similar conflicts erupted last year in Rakhine in northern Myanmar.
The Irrawaddy, a Myanmar newspaper published in Thailand, reported "anti-Muslim" riots are spreading from the center of the country. Thein Sein vowed late Monday to "make an earnest effort" to address the violence.
Myanmar earned praise from members of the international community for a series of democratic reforms that began with general elections in 2010. Dieng said there were serious risks remaining, however.
"The government of Myanmar must clearly demonstrate that it is serious about holding accountable those responsible for the past and present violence, regardless of their religious or ethnic affiliations," he said in a statement.