The regime has unleashed a deadly wave of violence as it struggles to quell nationwide protests against the February 1 ouster and arrest of civilian leader Aung San Suu Kyi.

The 75-year-old was due to have a court hearing on Wednesday in Myanmar's capital Naypyidaw, on criminal charges that could see her permanently barred from political office.

But her lawyer Khin Maung Zaw said the hearing was adjourned until April 1 because of problems with video conferencing caused by a junta-imposed internet shutdown.

In commercial hub Yangon, AP photographer Thein Zaw, 32 -- who was arrested last month while covering a protest -- was freed from Insein prison.

"I'm now on my way back home to meet with my mum. I'm in good health," Thein Zaw told AFP.

"The police officer who sued me withdrew his charge -- that's why they released me unconditionally."

The AP's vice president for international news Ian Phillips said the agency was "deeply relieved" at Thein Zaw's release.

He had been charged with "spreading false news", along with five other journalists who were arrested the same day and are still in custody.

Seperately, Polish photojournalist Robert Bociaga -- who was also arrested while covering protests -- was released after nearly a fortnight in detention, he told AFP Wednesday, adding that he was set to be deported.

- 'Silent strike' -

Thein Zaw's release came hours after more than 600 people held for protesting against the coup were freed from the same jail.

"We released 360 men and 268 women from Insein prison today," a senior prison official told AFP on condition of anonymity, before the AP photographer's release.

Lawyer Khin Maung Myint, who was at Insein prison for the hearing of two other clients, said 16 busloads of people left the jail at 10 am local time (0400 GMT).

"Some clients called me (after) informing me of their release," he told AFP.

Local media showed images of the prisoners on the buses flashing the three-fingered salute -- a sign of resistance for the anti-coup movement -- as people waiting outside the prison waved at them and returned the gesture.

Activists called for a nationwide "Silent Strike" on Wednesday, and streets were bare in the cities of Yangon and Naypyidaw.

In the southern city of Myeik, rows of dolls were set up along roads, holding up tiny signs reading "We need democracy" and "We wish for Mother Suu to be healthy".

- At least 20 children killed -

There was chaos overnight in Mandalay with barricades burning, arrests, homes raided by security forces, beatings and machine guns ringing out over multiple neighbourhoods, local media reported.

Three people were killed on Tuesday including seven-year-old girl Khin Myo Chit, shot dead at her home in Mandalay, according to the Assistance Association for Political Prisoners (AAPP), a local monitoring group.

Aid group Save the Children and AAPP both say that at least 20 people aged under 18 have been killed in the crackdown.

"We are horrified that children continue to be among the targets of these fatal attacks on peaceful protesters," Save the Children said in a statement.

"We once again call on security forces to end these deadly attacks against protesters immediately."

Up to 7,000 refugees are expected to flee the unrest in the country's urban centres by the end of April, according to the Karen National Union (KNU), an ethnic rebel group which controls territory in southeastern Karen state near the Thai border.

Hundreds of people have already fled to its areas of control, the KNU's general secretary Saw Tah Doh Moo told AFP.

Myanmar's junta on Tuesday defended its seven-week crackdown, insisting it would not tolerate "anarchy".

AAPP has verified 275 deaths since the coup, but warns the toll could be higher, and says more than 2,800 people have been detained.

Junta spokesman Zaw Min Tun put the death toll lower at 164, and branded the victims "violent terrorist people" at a Tuesday news conference in Naypyidaw.

- Suu Kyi graft claims -

Suu Kyi faces several criminal charges, including for owning unlicensed walkie-talkies and violating coronavirus restrictions by staging a campaign event last year.

She is also being investigated for corruption allegations.

Her lawyer says he has still not been able to speak to her privately.

The junta alleges the detained chief minister of Yangon confessed to giving Suu Kyi $600,000 in cash, along with more than 11 kilograms ($680,000 worth) of gold.