COLOMBO (Reuters) - The United Nations on Wednesday raised concern for the safety of Rohingya Muslim asylum seekers in Sri Lanka after Buddhist monks and hardline nationalists forced them to flee a U.N. shelter in the capital Colombo.  The refugees, who were detained in April along with two suspected Indian human traffickers in a boat off Sri Lanka s coast, are now in a camp in southern Sri Lanka to ensure their security after the incident in the capital. In Tuesday s incident, the Sri Lankan monks and nationalists stoned the shelter, prompting its 31 Rohingya occupants - mainly women and children - to flee for their own safety, witnesses said. No injuries were reported. In a statement, the U.N. High Commissioner for Refugees said  the incident was alarming, saying the refugees had been victims of violence and persecution in Myanmar, from which some 422,000 Rohingya have fled to nearby Bangladesh over the past month.  UNHCR emphasizes that (the) refugees ... need international protection and assistance. UNHCR urges the public and all those concerned with refugees to continue extending protection and to show empathy for civilians fleeing persecution and violence.   It said the Rohingya had been staying in Buddhist-majority Sri Lanka with the Colombo government s approval and UNHCR was providing assistance  until longer-term solutions can be found . President Maithripala Sirisena s government condemned the attack on the refugees as  shameful  and urged police to hunt down the perpetrators.  Witnesses said the monks stormed into the safe house chanting,  Rohingyas are terrorists  and accusing them of having killed Buddhist monks in Myanmar. The Rohingya group fled Myanmar in 2012 and lived in India as refugees for nearly five years before trying to migrate illegally to Sri Lanka, a lawyer representing them told Reuters.  Tension between Myanmar s majority Buddhists and the Rohingya, most of whom are denied citizenship, has exploded several times over the past few years as old enmities, and Buddhist nationalism, surfaced with the end of decades of harsh military rule. There has been an exodus of Rohingya from Myanmar s Rakhine state since Aug. 25, when attacks by Rohingya militants triggered a military crackdown that the United Nations has branded  ethnic cleansing . The authorities in Myanmar and Bangladesh each see the stateless Muslim minority as the other nation s problem.  