The United Nations rights chief has warned of possible crimes against humanity in Myanmar and said the country appeared to be heading towards a big conflict like the one ravaging Syria.

Michelle Bachelet urged countries to take immediate and decisive action to push the military leaders behind the 1 February coup in Myanmar to stop their "campaign of repression and slaughter of its people."

"I fear the situation in Myanmar is heading towards a full-blown conflict. States must not allow the deadly mistakes of the past in Syria and elsewhere to be repeated," she said in a statement.

Myanmar is in chaos and its economy paralysed since the military seized power from civilian leader Aung San Suu Kyi.

A crackdown against dissent has resulted in the civilian death toll reaching at least 710, including 50 children, according to a local monitoring group.

Meanwhile, ethnic armed rebel groups have stepped up attacks on the military and police in recent weeks, raising fears of Myanmar spiralling into broader civil conflict.

The army has retaliated with air strikes that have reportedly displaced thousands of civilians.

"The military seems intent on intensifying its pitiless policy of violence against the people of Myanmar, using military-grade and indiscriminate weaponry," Ms Bachelet said.

"There are clear echoes of Syria in 2011," she warned, referring to the start of a civil war that over the past decade has killed nearly 400,000 people and forced more than six million to flee the country.

"There too, we saw peaceful protests met with unnecessary and clearly disproportionate force.

"The state's brutal, persistent repression of its own people led to some individuals taking up arms, followed by a downward and rapidly expanding spiral of violence all across the country."

Police trucks block the road in front of the City Hall in Yangon

Ms Bachelet pointed out that her predecessor Navanethem Pillay had warned in 2011 "that the failure of the international community to respond with united resolve could be disastrous for Syria and beyond."

"The past 10 years have shown just how horrific the consequences have been for millions of civilians," she said.

Ms Bachelet pointed to "credible reports" indicating that Myanmar's Tatmadaw military forces opened fire with rocket-propelled grenades,fragmentation grenades and mortar fire in the southern city of Bago late last week.

At least 82 anti-coup protesters were reportedly killed in the crackdown.

Security forces also reportedly prevented medical personnel from helping the wounded and charged relatives a "fine" of around €75 to claim the bodies of those who were killed, the UN rights office said.

At the same time, it said, at least 3,080 people are detained across the country, while 23 people have reportedly been sentenced to death following secret trials, including four protesters and 19 others accused of political and criminal offences.

Ms Bachelet urged the international community to take action.

"Statements of condemnation, and limited targeted sanctions, are clearly not enough," the former Chilean president said.

"States with influence need to urgently apply concerted pressure on the military in Myanmar to halt the commission of grave human rights violations and possible crimes against humanity against the people."

A member of the Myanmar Fire Services uses a hose to wash Buddha statues with scented water during the traditional water festival in Sittwe, Rakhine State

Anti-coup protesters turned the country's New Year festival of Thingyan into a rallying point, painting pro-democracy messages on traditional clay pots and collecting flowers.

Many in the anti-coup protest movement have vowed to boycott water fight celebrations for the Thingyan festival, with some saying it would be disrespectful to have fun when so many have lost their lives and around 3,000 people are detained.

Last year's festivities were called off because of pandemic restrictions.

Protesters in parts of Yangon, Monywa and Bago painted traditional Thingyan pots with pro-democracy messages today before placing them on streets with flowers inside.

In Mandalay - Myanmar's cultural hub - people put pots and flowers on a golden stupa, with signs showing the three-fingered salute that has become a symbol of the resistance movement.

Young people in Mawlamyine, the fourth largest city, took to the streets early in the day while people marched with pots and flowers in the city of Dawei and small towns in Shan and Kachin states.

Meanwhile, security forces found and defused a bomb beneath the Myaynigone bridge in Yangon, a police source said.

Overnight, the junta announced a further 20 people were added to an arrest warrant list of 200 celebrities, including actors and singers, who are accused of spreading dissent against the military.

If convicted they could face three years' jail.