There has been a wave of online Chinese ultranationalism directed at Japan in recent years amid rising tensions between the two countries, especially over Tokyo’s support for Taiwan and territorial disputes in the East China Sea.

Some posts urged Chinese to “go against the Japanese and eliminate traitors” while calling to establish a “modern-day Yihetuan”, it said in a statement on Saturday night.

Yihetuan, also known as the “Boxers” from the martial arts they practised, were a Chinese nationalist secret society during the Qing dynasty (1644-1912) that supported imperial power and resisted Westernisation. Their slogan was “Support the Qing, destroy the foreigners”. The movement later led to the failed 1899-1901 Boxer Rebellion against Western and Japanese powers in northern China.

A right wing nationalist movement of the past that supported a monarchy being referenced by a small number of online trolls doing asshole things. Definitely not to be confused with general opinions of the greater Chinese population.

The measures were in line with the response from Beijing. In a commentary on Friday evening, Communist Party mouthpiece People’s Daily said that “Chinese people have the same standards on right and wrong”.

Probably an unnecessary use of the word "mouthpiece." At least for this situation, there's no need to give the negative connotation to the target audience of English native readers.