Demonstrators in Myanmar protesting against last month’s military coup have returned to the streets, undaunted by the killing of at least 38 people by security forces the previous day.

New protests were held in at least three areas of Yangon, the country’s largest city, which have been scenes of violence for the past few days.

Police again used force to try to disperse the crowds, according to social media accounts.

Protests also continued in Mandalay, the second-biggest city.

A formation of five fighter planes flew over the city on Thursday morning in what appeared to be a threatening show of force.

The UN special envoy for Myanmar, Christine Schraner Burgener, said 38 people were killed on Wednesday, describing it as “the bloodiest day” since the coup.

The death toll was the highest since the February 1 takeover, when the military ousted the elected government of leader Aung San Suu Kyi.

More than 50 civilians, mostly peaceful protesters, are confirmed to have been killed by police and soldiers since then.

The UN Security Council has scheduled closed-door consultations on Friday on calls to reverse the coup – including from UN secretary-general Antonio Guterres — and stop the escalating military crackdown.

Any kind of co-ordinated action at the UN will be difficult as two permanent members of the Security Council, China and Russia, are likely to veto it. Some countries have already imposed or are considering their own sanctions.

Ms Burgener said she warned Myanmar’s army that the world’s nations and the Security Council “might take huge strong measures”.

“And the answer was, ‘We are used to sanctions and we survived those sanctions in the past’,” she said.

When she also warned the army that Myanmar would become isolated, she said: “The answer was, ‘We have to learn to walk with only a few friends’.”

The coup reversed years of slow progress towards democracy in Myanmar, which for five decades had languished under strict military rule that led to international isolation and sanctions.

As the generals loosened their grip, culminating in Ms Suu Kyi’s rise to power after 2015 elections, the international community responded by lifting most sanctions and pouring investing into the country.

Ms Burgener said the army had been taken aback by the strong opposition, which has been led by young people.

“I think that the army is very surprised that it doesn’t work because in the past, in 1988 and 2007 and 2008, it worked,” she said, referring to previous violent crackdowns on uprisings against military rule.

Demonstrators have flooded the streets of towns and cities across Myanmar since last month’s coup, even though gatherings of five or more people are banned and security forces have repeatedly fired tear gas, rubber bullets and live rounds to disperse the crowds, and arrested protesters en masse.

Protesters in Mandalay flashed a three-fingered salute of resistance on Thursday as they rode their motorbikes to follow a funeral procession for Kyal Sin, also known by her Chinese name Deng Jia Xi, a university student who was killed as she attended a demonstration on Wednesday. Many thousands of people attended.

As part of the crackdown, security forces have also arrested more than a thousand people, including journalists, according to the independent Assistance Association for Political Prisoners.