Japanese media said on Tuesday that Japanese Prime Minister Yoshihiko Noda will send a letter to Chinese President Hu Jintao concerning the strained China-Japan ties.

The letter will be delivered later in the day by Tsuyoshi Yamaguchi, parliamentary senior vice-minister of foreign affairs, Japanese TV station Tokyo Broadcasting System reported.

On Monday afternoon, the Japanese flag of a car carrying the Japanese Ambassador Uichiro Niwa was reportedly pulled off by an unidentified person in Beijing.

The relevant authorities are seriously investigating the report that the flag of the ambassador's vehicle was ripped off, the Foreign Ministry spokesperson's office told Xinhua News Agency on Monday evening.

Officials of the Japanese embassy in China said that Niwa was not hurt in the attack, Kyodo News Agency reported.

The Chinese government always conscientiously fulfills the Vienna Convention on Diplomatic Relations to protect the safety of foreign embassies and personnel, the Chinese Foreign Ministry said.

The Japanese Embassy said in a press release it has filed a strong protest with the Chinese Foreign Ministry.