Security forces backed by armoured vehicles clash with a newly formed resistance group in the second-biggest city of Mandalay, resulting in at least six casualties, authorities and military sources say.

Fighting has flared across Myanmar since the February coup as people form
Fighting has flared across Myanmar since the February coup as people form "defence forces" to battle a brutal military crackdown on dissent. (AFP)

Four protesters and at least two officers have been killed as Myanmar soldiers battled an anti-junta civilian militia with small arms and grenades in the country's second city, authorities and military sources said.

Acting on a tip-off, security forces raided a house in Mandalay's Chan Mya Tharsi township on Tuesday morning, the junta's information team said in a statement, and were met with small arms fire and grenades.

Two officers were killed during the raid, military sources told AFP news agency, and at least ten were wounded.

Four "terrorists" were killed and eight arrested in possession of homemade mines, hand grenades and small arms, a junta spokesman said in a statement.

"We could hear artillery shooting even though our house is far from that place," a Mandalay resident told AFP.

Another four members of the self-defence group were killed when the car they were attempting to flee in crashed, the spokesman said, without providing details.

The United States' embassy in Yangon said on Twitter it was "tracking reports of ongoing fighting in Mandalay... We are disturbed by the military escalation and urgently call for a cessation of violence."

Fighting has flared across Myanmar since the February coup as people form "defence forces" to battle a brutal military crackdown on dissent, but clashes have largely been restricted to rural areas.

Hundreds dead since coup 

The mass uprising against the military putsch that toppled the government of Aung San Suu Kyi has been met with a brutal crackdown that has killed more than 870 civilians, according to a local monitoring group.

As well as the rise of local self-defence forces, analysts believe hundreds of anti-coup protesters from Myanmar's towns and cities have trekked into insurgent-held areas to receive military training.

But part-time fighters know the odds are stacked against them in any confrontation with Myanmar's military – one of Southeast Asia's most battle-hardened and brutal.

READ MORE: Myanmar rebels train anti-coup protesters for combat against junta

Suu Kyi back in junta court on sedition charges

On Tuesday, Suu Kyi appeared in a junta court on trial for sedition and for flouting Covid restrictions during an election her ousted party won in a landslide.

Under house arrest and invisible bar a handful of court appearances, Suu Kyi has been hit with an eclectic raft of charges, including accepting illegal payments of gold and violating a colonial-era secrecy law.

The court heard testimony she violated Covid-19 restrictions during elections last year that her National League for Democracy (NLD) party won in a landslide, her lawyer told reporters.

The special court in Naypyidaw also heard testimony on separate sedition charges.

Journalists were barred from the proceedings.

Brief meetings with her legal team have been the only channel to the outside world for Suu Kyi – who remains widely popular in Myanmar – since she was detained in February.

Junta leader Min Aung Hlaing has justified his power grab by citing alleged electoral fraud in the November poll and has threatened to dissolve the NLD.

Suu Kyi's lawyers have said they expect the trial to wrap up by July 26.

READ MORE: Myanmar teachers won't go back to class as junta reopens schools

Source: AFP