Children were among those killed and injured in airstrikes by Myanmar’s military on an ethnic rebel-controlled area in the country’s southeast, a humanitarian aid group said Tuesday, as junta forces stepped up their offensive in the region. Myanmar’s military, which seized power in a February 1 coup, has been conducting airstrikes in southeastern Karen state since Saturday night, forcing thousands of residents to flee into the jungles. Many of the villages targeted are controlled by the Karen National Union (KNU), an ethnic armed group that holds large swathes of territory in the borderlands. A 5-year-old boy died in a bombing on Sunday, and a 12-year-old girl was hit in the face by bomb shrapnel, according to relief organization Free Burma Rangers (FBR). The girl had come to Day Bu Noh village to attend school, the group said. A high school in Dwe Lo Township was destroyed in an airstrike on Monday, but no casualties were reported as the students were in hiding, FBR said. Then on Tuesday, six people were killed and 11 injured by airstrikes near Hsaw Hti township. In a statement Tuesday, the KNU condemned the Myanmar military’s bombing campaign. “Villagers, including underage children, have been killed by airstrikes,” the KNU statement said. “Many are injured.” CNN has not been able to independently verify these reports. Myanmar has been thrown into turmoil since Gen. Min Aung Hlaing ousted the elected government of Aung San Suu Kyi and installed a military junta two months ago. Protesters have taken to the streets nearly every day, and workers in various sectors including health care and transport have gone on strike, disrupting the economy. The military has responded by embarking on a systematic and bloody crackdown, shooting unarmed civilians in the street, while carrying out beatings, arbitrary detentions and nighttime raids on the homes of suspected opposition members. This weekend saw the bloodiest crackdown yet, with at least 114 people killed on Saturday. Residents fleeing the violence have fled to several neighboring countries, including Thailand and India. Myanmar security forces have killed at least 521 people since the coup, with more than 2,600 detained, according to advocacy group Assistance Association for Political Prisoners (AAPP). Rebel groups in ethnic states More than two dozen ethnic armed groups have been fighting against the Myanmar military – known as the Tatmadaw – and each other, for greater rights and autonomy on and off for 70 years. Fighting in some of these regions has increased since the coup. Many ethnic armed groups, including the KNU, have come out in support of the protests and condemned the military takeover. The KNU said it attacked a military outpost near the border with Thailand on Saturday morning. In its statement Tuesday, the KNU said it tookover the outpost “to stop the terrorizing of villagers and allow people to return safely to their communities.” The rebels said Myanmar military troops were now moving into KNU-held areas, despite a ceasefire in place since 2015. “Thousands of Burma military ground troops are advancing into our territories from all fronts,” the KNU statement said. “We have no other options left but to confront these serious threats posed by the illegitimate military junta’s army in order to defend our territory.” In a report in the military-controlled Global New Light of Myanmar Tuesday, Gen. Min Aung Hlaing accused the KNU of “dancing to the tune of countries and organizations” which oppose the junta. This weekend’s crackdown is the first time in 20 years airstrikes have been carried out in KNU-controlled territory, said David Eubank, founder of Free Burma Rangers. The group urged the international community to provide humanitarian help to its people fleeing the military’s “onslaught,” and to pressure the ruling junta to stop using weapons against civilians. “We are very concerned about the safety and security of our civilians,” said the statement. Fleeing across borders Thousands of people have fled from Myanmar to its neighboring countries, raising concern and alarm in the region about a potential influx of refugees. Since the air strikes, 3,000 people have attempted to cross the Salween River into Thailand and 2,000 were pushed back, according to the KNU. Activist group the Karen Women’s Organization (KWO), which operates within Karen state and refugee camps in Thailand, confirmed the air strikes had forced 10,000 people in the state from their homes, and 3,000 had crossed into Thailand. The Thai Ministry of Foreign Affairs confirmed that on Tuesday, the country provided medical treatment and other assistance to seven people who were injured while fleeing Myanmar. Six ambulances were deployed to take them to hospital, said the ministry in a statement. Assistance was also given to vulnerable groups like children and the elderly. “These people were unable to return across the border yesterday, despite their wish to return home they had also expressed their fear from air raids,” said the statement. “Authorities concerned have ensured that this particular group of people were well taken care of, and that they were prepared for their return back home when the situation is deemed safe.” Thailand’s Prime Minister Prayut Chan-o-cha said on Tuesday his government did not force back those who entered the country. “There are many people who have entered into certain villages (on Thai side), and when we found them, we talked to them. After we asked questions what are their problems in your country they said, there’s no problem,” Prayut said during a news conference. “We didn’t force them (to return) with guns,” Prayut added. “There is no way we will push them back if the fighting is still ongoing. But if there is no fighting now, can they return to their home?” He had previously said that though his government did not want refugees to cross the border, they were preparing for a potential influx. Thailand has hosted tens of thousands of refugees in nine main camps along its border with Myanmar for three decades, following armed conflicts, human rights abuses and persecution of ethnic minorities by the Myanmar military. Most of those who crossed the border over the weekend are from Mu Traw district, where the bombing has been concentrated. Many of those are people who have already fled their homes and are living in the Ei Tu Hta displacement camp. Hundreds have also trekked across western Myanmar to cross into the neighboring Indian state of Mizoram. A network of locals and activists have helped facilitate their crossing, and are providing shelter to many of those without family in India. The chief minister of the state has staunchly opposed deporting them back to Myanmar, telling CNN earlier this month, “They are not criminals.” However, the federal government has not publicly announced what it will do with the new arrivals. Meanwhile in China, an outbreak of Covid-19 has been blamed on those fleeing Myanmar. Yunnan province, which borders Myanmar to the south, detected nine Covid-19 cases on Tuesday, four of which are Burmese nationals. The Yunnan Health Commission launched a testing program across the city of Ruili, and locked down the city with suspended inbound and outbound travel. In a statement, the commission added that local authorities will crack down on illegal border crossings from Myanmar. Chinese officials also blamed smugglers from Myanmar for a surge in cases in September, with the Ruili police deputy director telling reporters that there were “Burmese asymptomatic cases illegally crossing into the Chinese border.” China, along with Russia, recently blocked the United Nations’ move to condemn the Myanmar military.