The military junta 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.

International condemnation has so far done little to quell the brutal crackdown, but the United States and Britain said Thursday it would impose sanctions against the highly secretive behemoth Myanmar Economic Holdings Ltd, which gives army chiefs access to enormous wealth.

"Today's sanctions target the military's financial interests to help drain the sources of finance for their campaigns of repression against civilians," UK Foreign Secretary Dominic Raab said.

Washington announced it was also imposing sanctions on Myanmar Economic Corporation Limited (MEC).

The Myanmar military "controls significant segments of the country's economy through these holding firms," said a US Treasury Department statement.

The opaque groups have their tentacles in industries as diverse as beer, tobacco, transportation, textiles, tourism and banking.

Protesters have continued calling for the military to step down, defying nighttime curfews to stage candlelight vigils for the dead, and taking to the streets early in dawn marches to avoid security forces.

A sunrise mobile rally on motorbikes in northern Kachin state saw the arrest of several demonstrators, which drew defiant protesters to the police station to demand their release.

But it turned deadly once the military arrived and shot into the crowd, leaving at least one dead, a resident said.

In the city of Hpa-An in southeastern Karen state, protesters were preparing sandbags around 6:00 am on Thursday (2330 GMT Wednesday) when scores of soldiers and police swooped in and tried to clear the streets using stun grenades.

"After that, they shot with rubber bullets as well as real bullets, about 50 shots," a protester told AFP by phone.

"A student got shot in the thigh by a live round and is now receiving medical treatment."

Early-bird protesters were also out in parts of Myanmar's commercial hub Yangon, wearing traditional ethnic outfits and waving the country's flag.

Some carried signs that said "Get out, terrorist dictator", according to local media.

- 'Distressed' -

International pressure from the UN, US and Britain has been building on the junta, but so far it has seemingly been ignored.

Britain and the US have already announced sanctions on the regime in recent weeks.

Regional powers Indonesia and Singapore on Thursday urged the junta to halt its use of lethal arms, as its foreign ministers met to discuss Myanmar.

Singapore's Vivian Balakrishnan said both nations were "distressed by the loss of human lives", but said the solution would have to come from within.

"Both Indonesia and Singapore... believe there should be no foreign interference but ASEAN (the 10-country bloc) stands ready to help in any way," he said.

Since the coup, more than 280 people have been killed, according to the Assistance Association for Political Prisoners -- a local monitoring group tracking the death toll and arrests.

But the junta puts the death toll as much lower at 164, and has branded the victims as "violent terrorist people".

A UN special rapporteur on human rights in Myanmar once again sounded the alarm Thursday on the country's situation, criticising the "slow pace of diplomacy".

"Conditions in Myanmar are deteriorating but they will likely get much worse without an immediate, robust, international response in support of those under siege," Tom Andrews said in a statement.

"I fear that the international community has only a short time remaining to act."

- 'We stand by the people' -

There are fears that Saturday -- Myanmar's Armed Forces Day, usually marked with a parade in Naypyidaw -- could be a flashpoint.

State-run media reported Thursday that police had arrested 14 Yangon youths caught fleeing the city for territories in Myanmar's east, which are controlled by ethnic armed militias.

So far, hundreds have fled to Karen state, where the rebel Karen National Union has sheltered hundreds of anti-coup activists escaping the junta.

In neighbouring Kayah state -- where the Karenni National Progressive Party (KNPP) holds control over part of the region -- scores have also arrived since the February 1 putsch to seek shelter, said its vice chair Khu Oo Reh.

"We stand by the people," he told AFP, adding that the power takeover has shone a light on the struggle of ethnic groups long agitating for autonomy in Myanmar.

"They (Bamar majority) have never shared the suffering of our people who have experienced it for over 70 years. Now they are starting to know and learn the bitterness of our people."