Thirty-eight people have been killed after security forces fired on pro-democracy protesters at multiple rallies across Myanmar today, according to United Nations special envoy, Christine Schraner Burgener.

The deaths come a day after neighbouring countries called for restraint and offered to help Myanmar resolve the crisis.

Myanmar has been in uproar since 1 February when the military launched a coup and detained civilian leader Aung San Suu Kyi.

The move ended the nation's decade-long experiment with democracy and sparked daily mass protests.

Ms Burgener said the UN must take "very strong measures" against the army to bring Myanmar back to democracy.

"I think the member states have to take very strong measures," she told reporters.

"I had a discussion with the army and I warned them that member states and the Security Council might take huge, strong measures.

"The answer was 'We are used to sanctions and we survived those sanctions in the past.'"

International pressure is mounting on Myanmar's military as Western powers have repeatedly hit the generals with sanctions.

The UK has called for a UN Security Council meeting on Friday.

But the junta has ignored the global condemnation, responding to the uprising with escalating strength.

The military has also hit half a dozen detained journalists with criminal charges that could see them spend up to three years in jail if convicted.

Police charge towards protesters in Yangon

Several cities in Myanmar saw bloody crackdowns on protesters by security forces today, including Monywa in the central Sagaing region.

Parts of the city of Yangon were transformed, with protesters using makeshift tyres and barbed wire barricades to block major roads.

Near the famed Sule pagoda intersection, protesters pasted printouts of junta leader Min Aung Hlaing's face on the ground - a tactic aimed at slowing down security forces who will avoid standing on the portraits.

A 19-year-old protester, engineering student Aung Myint Myat, died after being shot in Salin.

"It was my friend who was shot in his forehead and died in the hospital," said Min Pyae Phyo.

"They shouldn't have used such lethal force against the peaceful protesters. I won't forget and forgive them the rest of my life," he added.

Police fired tear gas at protesters in Mandalay

A demonstration in Myingyan turned deadly when security forces deployed tear gas, rubber bullets and live rounds against protesters carrying red home-made shields emblazoned with the three-finger salute - a symbol of resistance for the anti-coup movement.

Local media in northern Kachin state also reported similar scenes of violence, publishing images of police bearing down on protesters in Hpakant. 

"Some were hit with rubber bullets and some were suffocating because of tear gas," a doctor said.

Protesters stand guard on a street in Yangon

Today's violence came on the heels of news that six Myanmar journalists would be charged under a law prohibiting "causing fear, spreading false news, or agitating directly or indirectly a government employee", according to their lawyer Tin Zar Oo. 

Among them is Associated Press photographer Thein Zaw, who was arrested on Saturday as he covered an anti-coup demonstration in Yangon.

Video emerged today of him being held in a chokehold by police as he was handcuffed.

The other five are from Myanmar Now, Myanmar Photo Agency, 7Day News, Zee Kwet Online news and a freelancer.

The maximum sentence for the offence has been increased from two years to three, following amendments made by the junta last month after it took power. 

According to the Assistance Association for Political Prisoners (AAPP) monitoring group, more than 1,200 people have been arrested since the coup, with about 900 still behind bars or facing charges.

But the real number is likely far higher, as state-run media reported more than 1,300 people were arrested on Sunday alone.

Yesterday, media reported that about 500 have been freed in Yangon.