China has lodged a protest with neighboring Myanmar, saying a bomb dropped by a Myanmar warplane hit a Chinese border province and killed four people.

The Myanmar government is fighting ethnic Chinese rebels in the country's Kokang region on the border with China. The upsurge in fighting in recent weeks has sent thousands of people fleeing across the border into China's Yunnan province.

The Chinese foreign ministry said in a statement Saturday that Liu Zhenmin, a vice foreign minister, summoned Myanmar Ambassador Thit Linn Ohn in Beijing, and strongly condemned the killings of civilians.

The official Xinhua News Agency says the bomb hit a sugarcane field in the Chinese border city of Lincang, killing four people working there on Friday and wounding nine others.