A series of airstrikes by Myanmar’s military has driven thousands of people across the country’s border with Thailand, adding a new dimension to an already volatile and deadly crisis. The strikes in areas populated predominantly by ethnic Karen people began on Saturday. Since then an estimated 3,000 villagers have fled across the Salween River into Thailand and an unknown number have become internally displaced in the jungles on the Myanmar side of the river. “There were big explosions, and many houses and buildings burned down,” said Naw Wah Khu Shee, the director of Karen Peace Support Network. She said at least three people were killed in Saturday’s strikes, including one girl aged seven or eight, and eight were badly injured. The government has battled Karen fighters on and off for years as it has with other minority ethnic groups seeking more autonomy, but the airstrikes are a worrying development at a time when the junta is violently suppressing anti-coup protests. More than 100 people, including several children, were killed in cities across the country at the weekend. Leaders of the resistance to last month’s military coup that toppled Myanmar‘s elected government are calling for the Karen and other ethnic groups to band together and join them as allies in a “federal army”, which would add an armed element to their struggle. “The situation is evolving into an all-out civil war,” said one Mandalay-based protester, who requested anonymity for fear of reprisals by the military. “I see comrades with vests, gas masks, helmets and protective eyeglasses, armed with makeshift weapons. Their equipment provides no protection against live ammunition, and their slingshots and swords deal next to no damage against the fascists, and yet they keep on fighting,” the protester said. Ethnic armed groups have voiced reciprocal support for the protesters, with one commander of the Karen National Liberation Army (KNLA) telling the news agency Myanmar Now: “Their bullying and killing of unarmed civilians across Myanmar is against our revolutionary force’s beliefs. We cannot accept inhumane acts, not only in [Karen state], but also in other areas.” The airstrikes began several hours after a KNLA brigade seized a military base, killing 10 soldiers and taking at least eight captive, according to an online site that carries official information from the Karen National Union. The report said one Karen guerrilla died. The air attacks represent the most significant escalation in the conflict between the army and the KNLA in more than a decade. The army had not deployed airstrikes against the KNLA since 1995, when the previous junta overran the headquarters of the Karen National Union, the movement’s political arm, in the now-abandoned village of Manerplaw. About 2,000 refugees fleeing Thailand had been pushed back, two activist groups said on Monday, but Thai authorities said the army was taking care of them on the border. Video showed villagers carrying their belongings boarding boats under the watch of Thai officials. Authorities blocked Reuters reporters from accessing the area. “There’s still fighter jets over the area,” Mark Farmaner, the head of Burma Campaign UK, told Reuters. “Thailand’s heartless and illegal act must stop now,” tweeted Sunai Phasuk, a senior researcher on Thailand for Human Rights Watch. Thichai Jindaluang, the governor of Thailand’s Mae Hong Son province, said the refugees were not being pushed back. State media reported they were in a safe place on the fringes of the border in Mae Sariang and Sop Moei districts. A Thai provincial official from Mae Hong Son who declined to be named said the group was “in Thai territory by the Salween River but they haven’t come further. It’s under army management.” Thailand’s prime minister, Prayuth Chan-ocha, said earlier on Monday his government was preparing for an influx of displaced people from Myanmar. “We don’t want to have an exodus into our territory, but we will observe human rights, too.” On Saturday, more than 100 people were killed in and around demonstrations throughout the country on the bloodiest single day since the coup. As the death toll rises, incidents of indiscriminate shootings are emerging. In central Myanmar, a 14-year-old girl was shot dead in her home, according to her father, as security forces sprayed a neighbourhood with bullets. A graphic video from the ruby mining town of Mogok shows a boy who had been shot in the face. “Don’t touch it, raise your head. Help him lie down,” says an onlooker as others curse at the police. On Sunday the violence continued as security forces fired automatic weapons in Yangon’s South Dagon Township, where a two-year-old who was indoors was hit in the ear by a bullet, according to the local news outlet Khit Thit Media. As security forces blocked the area, medics struggled to provide aid. Reuters contributed to this report