China sent fighter jets to patrol its border with Myanmar after a bomb dropped by a Myanmar warplane killed four Chinese in southwestern Yunnan province, state media reported March 14.
The bomb hit a sugarcane field in Lincang city on March 13, killing four workers and injuring nine others, China's official news agency Xinhua said.
It came days after China warned of escalating violence near the border following a surge in ethnic conflict in the remote Kokang region in Myanmar's northeastern Shan state.
The People's Liberation Army Air Force on March 13 sent several fighter jets to "track, monitor, warn and chase away" Myanmar military planes flying close to China's border, air force spokesman Shen Jinke was quoted by Xinhua as saying.
Chinese Deputy Foreign Minister Liu Zhenmin summoned the Myanmar ambassador to Beijing, Thit Linn Ohn, on the night of March 13 to protest against the deaths, the agency said.
Liu urged Myanmar to "thoroughly investigate" the case and "take immediate and effective measures to prevent recurrence of such incidents", said Xinhua.
He called on the Myanmar authorities to "safeguard the security and stability in the border areas between China and Myanmar", the agency added.
China's foreign ministry said earlier this week that a house in Yunnan had been hit by shelling from across the border in Myanmar, where the military are fighting rebel forces.
Last month, Myanmar declared a state of emergency in Kokang in response to the conflict, which began on February 9.
The unrest has virtually emptied the main Kokang town of Laukkai, the epicentre of the fighting, with streets in the once-bustling frontier community transformed into a battleground.
More than 30,000 people have fled from Myanmar into Yunnan province, according to Xinhua.