BEIJING - China and a Myanmar working group arriving at the China-Myanmar border on Sunday are investigating a bombing that killed four Chinese, China's Foreign Ministry confirmed on Monday.

A bomb dropped by a Myanmar warplane hit a sugarcane field in the southwestern Chinese city of Lincang, which borders conflict-hit Myanmar, killing four people and injuring nine others on Friday afternoon.

China has lodged serious complaints to Myanmar through different channels and Myanmar has expressed sorrow for the Chinese casualties, saying it will investigate the bombing and properly handle the aftermath, Foreign Ministry spokesman Hong Lei said at a daily news briefing.

The conflict in north Myanmar's Kokang region has lasted for over a month, severely impacting the border region's peace and stability, Hong said.

He urged conflicting parties to "take China's concerns seriously" and show restraint so as to restore the order at the border.

China has both the responsibility and ability to safeguard the stability of its border areas with Myanmar, Premier Li Keqiang said on Sunday while Chinese fighter jets patrolled the border to "track, monitor, warn and chase away" Myanmar military planes flying close to Chinese territory.