Naoto Kan spoke in parliament, yesterday, stating that "We told the Chinese authorities (the demonstrations) were regrettable and strongly urge (China) to ensure the safety of Japanese nationals and firms."
Mr Kan's remarks follow reports that several Japanese business premises were damaged during demonstrations in Chinese cities (Chengdu, Xi'an, Zhengzhou and Mianyang) in support of China's claims to disputed islands in the East China Sea and over Naoto Kan's support for the release of Liu Xiaobo.
The Japanese news agency, Kyodo, reported that protesters in Sichuan threw stones at a Japanese restaurant and broke the windows of Japanese-made cars. However, Chinese officials have done little to condemn the protest and vandalism. A Chinese foreign ministry spokesman Ma Zhaoxu said it was "understandable that some people expressed their outrage against the recent erroneous words and deeds on the Japanese side."
This comes as China steps up its campaign against the Nobel committee for awarding Liu Xiaobo with the Peace Prize, earlier this month.
The Global Times - the tabloid sister publication of the People's Daily, the ruling Communist party's mouthpiece - accused the Oslo-based committee of provoking a "serious ideological clash" between Beijing and the West. It cited a survey conducted by its own polling centre stating that nearly 6 out of 10 people believes that the prize should be withdrawn from Liu and a officially apology should be given to China.
"It is hoped the Nobel committee will reflect on their poor choice and apologize to the Chinese public," the newspaper said. Furthermore it stated that "The award is not a scarlet letter over China's forehead as the committee intended to see."
The official Xinhua news agency had added to the barrage on Sunday, saying in an editorial: "In what ways have Liu's actions contributed to human rights progress for China's 1.3 billion people?"
Dissidents and rights lawyers across the nation have reported being under increased surveillance or restrictions since the announcement.
The United States, the European Union and Japan have called for Liu's release.