Malaysian police have detained more than 900 Myanmar nationals in the capital Kuala Lumpur after a series of deadly clashes between Buddhist and Muslim groups.
Amar Singh, Kuala Lumpur's deputy police chief, says he doesn't want the violence to spread into Malaysia.
"The operation is to send a clear message to stop this nonsense," he said.
Police say four people have been killed and several others seriously injured in violence suspected to be linked to ongoing ethnic tensions in Myanmar.
U Maung Hla, head of the Burma Refugee Organisation in Malaysia, says violence between Myanmar refugee communities in Malaysia is not uncommon and is "sometimes due to religion".
Police have not provided details on the attacks but Malaysian media reports have suggested Buddhists came under attack from their Muslim countrymen seeking vengeance over violence in Myanmar.
The victims of religious tensions in Myanmar have mostly been Rohingya Muslims, but authorities in Malaysia say the victims in their country are Buddhists.
Violence against Rohingya Muslims, labelled by the United Nations as one of the world's most persecuted minorities, erupted in western Rakhine state last year and has spread across the country.
Thousands of the Muslim minority have escaped the violence and harsh living conditions by fleeing to Muslim-majority Malaysia.
The UNHCR says about 23,000 Rohingya Muslims are registered as refugees in Malaysia, but Malaysian authorities estimate more than 80,000 Myanmar nationals are living in the country