Thailand scrambled F-16s after a Myanmar jet involved in clashes with anti-coup fighters violated its airspace, officials said Thursday, as a regional envoy urging dialogue visits Yangon.
Fighting in eastern Myanmar has escalated since a putsch last year ousted a civilian government led by Aung San Suu Kyi, with thousands fleeing to Thailand to escape the violence according to the United Nations.
The conflict has sparked concern among Myanmar's neighbours, with a special envoy from regional block the Association of Southeast Asian Nations (ASEAN) beginning a visit on Wednesday to try to kickstart talks between the army and the opposition.
Bangkok deployed two fighter planes after "an unidentified aircraft crossed into Thailand in Tak province" before disappearing from radar, the Royal Thai Air Force said in a statement.
Thailand's air attache in Yangon has been asked to "coordinate with related agencies in Myanmar to send a warning and find preventive measures in the future", the air force added.
An official in Tak province told AFP that "a few bullets" had landed across the border in Thailand during fighting in Myanmar on Wednesday.
"We have sent a warning message to Myanmar yesterday and today" regarding the air incursion, said the official, who requested anonymity.
Authorities in Tak were providing basic shelter and food for around 300 people who had fled across the border, he said.
Myanmar's military has carried out airstrikes and artillery shelling during five days of "fierce fighting" in neighbouring Kayin state, said Major General Saw Nerdah Mya of the Karen National Defence Organisation, one of a number of armed groups resisting the country's security forces.
The clashes come as Cambodian foreign minister and ASEAN envoy Prak Sokhonn visits Myanmar for five days in an attempt to revive stalled diplomacy between the junta and rebels.
There are no details on who he will meet but the junta has said he will not be allowed to see Suu Kyi, who was moved from house arrest to solitary confinement in jail last week.
Almost 700,000 people have been forced to flee their homes since the toppling of Suu Kyi's government last year, the UN said in May.
Following the coup dozens of "People's Defence Forces" (PDF) have sprung up to fight the junta, surprising the military with their effectiveness, analysts say.
Kayin state near the Thai border has seen heavy fighting, with PDF fighters conducting operations alongside troops from the Karen National Defence Organisation, an established rebel group who have expressed support for anti-junta fighters.