Thousands have crossed into Thailand fleeing the latest round of violence between the Myanmar military and the KNU.
Myanmar's military has carried out more airstrikes on a rebel-controlled area near the Thai border, in the latest escalation of violence that has sent hundreds fleeing into Thailand.
The Karen National Union (KNU) said the military launched at least two airstrikes and fired some artillery rounds on an area under its control near the Thai-Myanmar border late on Thursday.
A Reuters reporter at Mae Sot, a Thai border town some 10 miles from where the air strikes reportedly took place, heard several explosions on Thursday evening at around 11 pm local time.
A spokesman for the Myanmar's military junta did not answer calls seeking comment.
Fresh fighting between the Myanmar military and the KNU broke out last week and more than 4,200 people have crossed into Thailand since the violence began, Thailand's foreign ministry said. Civil society groups have said the number of displaced is as high as 10,000.
KNU spokesman Saw Taw Nee said that the airstrikes have further displaced more civilians living in the area and repeated his group's call for the international community to establish a no-fly zone in the area.
Statements of concern
Myanmar has been in turmoil since the military ousted a civilian government led by Nobel laureate Aung San Suu Kyi on February 1, triggering protests and sporadic clashes in the countryside between anti-junta militia and the army.
Thailand's foreign ministry spokesman Tanee Sangrat said at a press conference on Friday that Thailand was concerned about the latest violence in Karen state that also impacted Thai people living along the border.
Several foreign envoys to Myanmar, including from the EU, Britain and the United States, issued a joint statement on Friday calling for an end to "indiscriminate attacks" in Karen state and elsewhere by the military.
"The recent attacks on civilians in Karen State, including the shelling of villages, are a violation of International Humanitarian Law and must stop," they said.