YANGON, Myanmar: A senior Myanmar official on Sunday denied Chinese accusations that one of his country’s warplanes crossed China’s border and dropped a bomb that killed four farmers during fighting with Myanmar rebels.

The official, from Myanmar’s presidential office, said his government regretted the deaths and suggested it could have been the work of a group seeking to create confusion. He also promised “full cooperation” with Beijing into the incident, which has tested generally good ties that have been strained in recent years by Myanmar’s perceived shift toward the US

The farmers’ deaths Friday occurred as Myanmar’s government stepped up its fight against ethnic Chinese rebels in the country’s Kokang region along China’s southwestern border.

The official, who spoke on condition of anonymity, cited radar and GPS records as proof that Myanmar fighter jets did not stray into Chinese territory. He also said Yangon always informs Beijing of its airstrikes in the border region beforehand.

Myanmar state television reported that Myanmar’s military and Chinese authorities began an investigation Sunday at the site of the incident. Beijing strongly protested the bombing and said it had sent fighter jets to warn off further intrusion.

Geng Yansheng, spokesman for China’s National Defense Ministry, said Saturday that Myanmar warplanes had intruded “multiple times” and that China would take “decisive measures” should they cross over again. Fan Changlong, vice chairman of the ruling Chinese Communist Party’s Central Military Commission, demanded that Yangon seriously investigate the incident, punish those responsible and apologize to the victims’ families.