Violence broke out on the streets of the commercial hub of Yangon on Thursday after some in a crowd of about 1,000 military loyalists attacked pro-democracy supporters and media.
Several people were beaten by groups of men, some armed with knives, others firing catapults and hurling stones, witnesses said. At least two people were stabbed.
In a separate incident, riot police launched a crackdown overnight, fired tear gas into the Tamwe neighbourhood of Yangon to disperse a crowd protesting the replacement of a local official by the military.
Residents later said they heard repeated shots and that police had remained in some parts of the district until around 2:00am on Friday.
Military chief General Min Aung Hlaing says authorities are using minimal force. Nevertheless, at least three protesters and one policeman have been killed in violence.
The Southeast Asian country has been in crisis since the army seized power and detained the civilian government leader Aung San Suu Kyi and much of her party leadership after the military complained of fraud in a November election.
There have been daily protests and strikes by pro-democracy supporters for about three weeks, often drawing hundreds of thousands of people across the diverse nation stretching from the country.