June 17 (Reuters) - A Myanmar ethnic political group fighting the army in the east has pledged to investigate junta accusations that its forces abducted a group of 47 people and killed 25 of them last month. Ethnic conflicts in Myanmar"s borderlands have flared anew since a coup on Feb. 1, and this week junta-controlled media reported fighters belonging to the Karen National Defence Organisation (KNDO) had committed the atrocity. The Karen National Union, the KNDO"s political wing, said in a letter dated June 16 its investigation would establish the truth. "The Karen National Union follows the Geneva Convention which doesn"t accept killing civilians during armed fighting," it said. The state-run Global New Light of Myanmar newspaper and army controlled Myawaddy Television this week showed pictures of what appeared to be 25 bodies in a forest clearing. They said the men had been working on a bridge in the Myawaddy District and were abducted on May 31 in a group that also included 10 children and six women. The newspaper reported seven bodies were found on June 11, one burnt and the others with hands tied behind their backs and the other 18 bodies were found the next day. read more A video shared on social media that purports to record one of the killings shows a bound man being repeatedly stabbed before his throat is slit and body mutilated. Some voices in the Karen language are heard calling for the killer to stop while others cheer him on. Reuters has not verified the authenticity of the video. The United Nations General Assembly is set on Friday to call for a stop to the flow of arms to Myanmar and urge the military to respect November election results and release political detainees, diplomats said. read more Myanmar has been in crisis since the coup and the generals have struggled to impose order, blaming the violence on "terrorists" and arresting thousands of people, including teachers, doctors and journalists. The Frontier Myanmar magazine said its managing editor Danny Fenster, an American, appeared at a special court session in prison on Thursday, charged with incitement. "We are shocked and frustrated that he has been detained for no apparent reason," Frontier said. Myanmar"s state-run MRTV made no mention of the court appearance in its nightly news bulletin In Washington, U.S. State Department spokesman Ned Price called on Myanmar to grant consular officials access to Fenster and to ensure proper treatment while he remains detained. "Our consular officers in Burma have sought to visit Daniel but we have not been afforded access to him by regime officials," Price told reporters on a briefing call. Though the bulk of international criticism has been directed at the junta, concerns are growing about the conduct of rebel forces and recently formed guerrilla movements and their impact on civilians. read more The United Nations in Myanmar said on Thursday it was alarmed by recent acts of violence that illustrated a "sharp deterioration of the human rights environment". It highlighted the discovery of the Myawaddy mass graves and the burning of Kin Ma village in Magway Region this week that witnesses said was carried out by security forces. The U.S. embassy in Myanmar on Thursday described the razing of Kin Ma as "horrific acts" consistent with past military atrocities. MRTV in its nightly newscast ascribed the razing to "terrorists" and said many media outlets were peddling fake news by blaming the fire on security forces. read more