Bangkok, Thailand (CNN) -- Myanmar has alarmed Washington and the United Nations after it admitted carrying out airstrikes against rebel fighters in the northern state of Kachin. The conflict between the Myanmar military, which repressively ruled the southeast Asian nation for decades, and the Kachin Independence Army (KIA) has escalated in the past two years, displacing large numbers of civilians, according to human rights groups. Watch: Economic potential in Myanmar Recent steps toward greater democracy and civil liberties in Myanmar under the government of President Thein Sein, a former military official, have prompted the United States and other countries to lift most of the sanctions that had been squeezing the country's economy.
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NEW: U.S. photojournalist says he has seen repeated airstrikes and heavy shelling
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Myanmar says it used "air attacks" on Kachin rebels this week
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The conflict in the northern region has intensified recently, rights groups say
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The United States says it is "deeply troubled" by the airstrikes
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But the @placeholder government expressed concern Wednesday after authorities in Myanmar said they had used air attacks in clashes with KIA fighters this week.
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But the U.S. government expressed concern Wednesday after authorities in @placeholder said they had used air attacks in clashes with KIA fighters this week.
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Attempts to reach a @placeholder spokesman for comment were unsuccessful Thursday.
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Read more: From Burma to @placeholder: Land of rising expectations