The territorial violation by China is the latest in a series of events amplifying tensions between Beijing and Japan.

A Chinese military surveillance plane breached Japanese airspace off the country’s southwestern coast on Monday, marking what Japan’s defense ministry described as the first known incursion by China’s military into its territorial airspace.

According to a ministry official, a Chinese reconnaissance aircraft briefly entered Japanese territory near Nagasaki Prefecture around 11:30 a.m. on Monday. In response, Japan’s Self-Defense Force put fighter jets on high alert and issued a warning to the Chinese aircraft.

While Chinese planes frequently appear in international airspace around Japan, this incident represents the first confirmed entry of a military aircraft into Japan’s territorial airspace.