Two warplanes "launched an air strike and aerial gunfire" followed by rockets from helicopters, says governor of Thailand's Mae Hong Son province, which borders Myanmar's Karen state, marking a second day of assault.
Myanmar's military has launched air assaults for the second day in a row into rebel-held territory where an army base was stormed by Karen fighters.
Fresh strikes came after gunfire was heard from neighbouring Thailand, a Thai official said on Wednesday as fighting escalates along the border.
Rebels of Karen National Union (or KNU) on Tuesday attacked and razed an army base on the banks of the Salween River — which demarcates a border between Thailand and Myanmar — and the military retaliated with air offensives.
On Wednesday, gunfire and bomb explosions could once again be heard around 9 am near Myanmar's Dar Gwin military base — located just north of yesterday's skirmish.
"It is suspected that (Myanmar) soldiers opened fire to protect their base," said a statement from Sithichai Jindaluang, the governor of Mae Hong Son province in Thailand which borders Myanmar's Karen state.
Two Myanmar military airplanes then "launched an air strike and aerial gunfire," followed by rockets fired from helicopters around noon, he said.
The governor added that 68 Myanmar residents crossed into Thailand this morning for refuge.
The day before, a 45-year-old Myanmar national had crossed over in the evening after Tuesday's fighting to seek medical help for his wounded wrist. He is now "stable."
Turmoil since February
Myanmar has been in turmoil since the junta ousted civilian leader Aung San Suu Kyi in a February 1 coup, its power grab angering much of its population.
The anti-junta movement has also garnered some support from some ethnic rebel groups, which controls territory along Myanmar's border regions.
KNU, one of the most prominent, has been among the junta's most vocal opponents — blasting the junta for violence against anti-coup protesters.
Clashes with the military in KNU's territory along the eastern border have increased since February 1, with the junta deploying air assaults last month — the first instance in Karen state in over 20 years.
No casualty confirmed yet
KNU's head of foreign affairs Padoh Saw Taw Nee confirmed the air raids, but said their soldiers "did not attack anything today".
He also criticised the junta for launching air assaults on an area where there are civilians.
"This is not the proper way for them to retaliate because the air strikes is extensive power compared to the might of (KNU's militia)," he told AFP news agency.
"They need to target military, but now all we see are civilians getting hurt."
Both the Thai governor and KNU could not confirm any casualties from Wednesday's air raids.
More than 24,000 people have been displaced from their homes since the military launched its first air strikes in the area last month.
Within Myanmar, the junta's security forces have killed more than 750 civilians since February 1, according to a local monitoring group tracking the death toll.
Meanwhile, Myanmar's pro-democracy unity government, which includes members of parliament ousted by the military coup, told Southeast Asia's regional bloc that it will not engage in talks until the junta releases all political prisoners.
The 10-member Association of Southeast Asian Nations (ASEAN) has been trying to find a path for Myanmar out of a bloody crisis and has called for an end to violence and talks between all sides.
But the junta has already declined to accept proposals to resolve the crisis that emerged from an ASEAN summit last weekend that was attended by Myanmar's Senior General Min Aung Hlaing, but no-one from the civilian side.
The pro-democracy National Unity Government (NUG), formed this month by opponents of the military, said ASEAN should be engaging with it as the legitimate representative of the people.
"Before any constructive dialogue can take place, however, there must be an unconditional release of political prisoners including President U Win Myint and State Counsellor Daw Aung San Suu Kyi," the N UG prime minister, Minister Mahn Winn Khaing Thann, said in a statement.
There was no immediate comment from any senior officials in ASEAN.
Win Myint, Suu Kyi and others have been detained since the coup, which the military launched as Suu Kyi's government was preparing for a second term after sweeping a November election.
The military said it had to seize power because its complaints of fraud in the election were not being addressed by an election commission that deemed the vote fair.
Pro-democracy protests have taken place in cities and towns across the country since the coup.
Alarmed by the turmoil in one of its members, ASEAN held a meeting on Saturday in the Indonesian capital with the leader of the junta in a bid to press him to end the crisis.
ASEAN did not invite a representative of Suu Kyi's ousted government.
ASEAN leaders said after the meeting they had reached a "five-point consensus" on steps to end violence and promote dialogue between the rival Myanmar sides.
ASEAN legitimising junta?
The junta later said it would give "careful consideration" to ASEAN's suggestions, which included appointing an envoy to visit Myanmar, "when the situation returns to stability" and provided that ASEAN's recommendations facilitated the junta's own roadmap and served the country's interests.
Activists had earlier criticised the plan, saying it helped to legitimise the junta and fell far short of their demands.
In particular, it did not call for the release of Suu Kyi, 75, and other political prisoners.
The Assistance Association for Political Prisoners advocacy group says more than 3,400 people have been detained for opposing the coup.
The NUG is largely made up of ousted members of parliament together with politicians representing ethnic minorities and pro-democracy protest leaders.
Protesters marched in support of the NUG in the second city of Mandalay on Wednesday, the Myanmar Now media outlet reported.