Uichiro Niwa, Japan’s ambassador to China, experienced an attack on his car in Beijing around 4 p.m. local time, Tokyo-based Kyodo News reported, citing officials in Japan’s embassy in Beijing. The report said that Ambassador Niwa was unhurt but the perpetrator ripped the Japanese flag from the car. Japan’s embassy has “filed a strong protest with the Chinese Foreign Ministry,” according to Kyodo News.

The attack took place in the backdrop of growing tensions between Tokyo and Beijing over islands in the East China Sea, which China calls the Diaoyu Islands and Japan refers to as the Senkaku Islands. Earlier this month 14 people from Hong Kong landed on the islands in order to demand Chinese sovereignty over them. Japanese authorities detained 7 of the activists but later released them.

In response to the Chinese activists’ landing, 10 Japanese citizens- including 5 local Assemblymen- swam to the islands and hoisted the Japanese flag. Beijing strongly condemned the move, with a Chinese Foreign Ministry spokesperson saying the islands were part of China’s “inherent territory”.

There were some signs the issue was dissipating. Besides releasing the 7 Chinese activists it detained, Japan’s Central government rejected a request from Tokyo’s metropolitan government to land on the Islands in order to survey them. The local government accepted the rejection to land but said that it would survey the islands from the surrounding waters. Tokyo’s mayor, Shintao Ishihara, previously declared his intent to purchase the islands.

The attack on Ambassador Niwa’s car likely ended any hope that the tensions would soon blow over. China has remained silent on the attack at this time of this writing.

Zachary Keck is the Assistant Editor of The Diplomat.