Myanmar has been in turmoil since the army seized power on Feb. 1 and detained 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 about three weeks of daily protests and strikes and students planned to come out again in the commercial hub of Yangon on Thursday.
But before many opponents of the coup gathered, about 1,000 supporters of the military turned up for a rally in central Yangon.
Some of them threatened news photographers, media workers and witnesses said, and scuffles soon escalated into more serious violence in several parts of the city centre.
Some military supporters were photographed with clubs and knives. Some threw stones and fired catapults, witnesses said, and several people were beaten by groups of men.
Video footage showed several apparent supporters of the military, one wielding a knife, attacking a man outside a city-centre hotel.
Emergency workers helped the man as he lay on the pavement after his attackers moved off but his condition was not known.
“Today’s events show who the terrorists are. They’re afraid of the people’s action for democracy,” activist Thin Zar Shun Lei Yi told Reuters.
“We’ll continue our peaceful protests against dictatorship.”
The violence will compound worries about a country largely paralysed by protests and a civil disobedience campaign of strikes against the military.
Earlier, police blocked the gates of Yangon’s main university campus, stopping hundreds of students inside from coming out to demonstrate.
Doctors were also due to hold a protest as part of a so-called white coat revolution.
Meanwhile, Facebook said that due to the risks evident from the “deadly violence” seen since the coup it had banned the Myanmar military from using its Facebook and Instagram platforms with immediate effect.
The spokesman for the ruling military council did not respond to a Reuters telephone call seeking comment.
The security forces have shown more restraint compared with earlier crackdowns against people who pushed for democracy during almost half a century of direct military rule.
Military chief General Min Aung Hlaing says authorities are following a democratic path in dealing with the protests and police are using minimal force, such as rubber bullets, state media reported.
Nonetheless, three protesters and one policeman have been killed in violence.
A rights group said as of Wednesday 728 people had been arrested, charged or sentenced in relation to the pro-democracy protests.
The army stepped in to oust the government saying military complaints of fraud in a Nov. 8 election, swept by Suu Kyi’s party as expected, had been ignored.
The election commission said the vote was fair. The army said its action was within the constitution and it promised to hold a new election after reviewing voter lists.
Suu Kyi has been detained incommunicado since the coup, at her home in the capital, Naypyitaw, but her party says its November victory must be respected.
The question of whether to hold a fresh election has emerged at the centre of the first diplomatic efforts to find a path out of the crisis, with Indonesia taking the lead within the Association of Southeast Asian Nations (ASEAN).
Its foreign minister said on Wednesday she had held intensive talks with the Myanmar military and representatives of the ousted government.
The minister, Retno Marsudi met Myanmar’s military-appointed foreign minister, Wunna Maung Lwin, for talks in the Thai capital earlier in the day.
But Indonesia’s intervention has raised suspicion among opponents of the coup in Myanmar who fear it will confer legitimacy on the junta and its bid to scrap the November election.
Retno told reporters the wellbeing of the people of Myanmar was the top priority.
“We ask for everybody to use restraint and not resort to violence,” she said after talks with the Myanmar minister and her Thai counterpart, Don Pramudwinai.
A Reuters report this week cited sources as saying Indonesia was proposing that ASEAN members send monitors to ensure the generals stick to their promise of fair elections.
The military has not given a time frame for an election although it imposed a one-year state of emergency when it seized power.
Retno did not mention an election but emphasised “the importance of an inclusive democratic transition process”.
The crisis has restored Myanmar’s reputation as the problem member of the 10-country ASEAN and the diplomatic scramble by its neighbours comes as wider international concern is growing.
The United States, Britain and others have imposed limited sanctions aimed at members of the junta and military businesses.