BEIJING -- Chinese mainland strongly protested on Friday against the visit to Japan by Taiwan's "army commander in chief" Hu Chen-pu, urging Japan to seriously observe the one-China policy.

"The Japanese government allowing Hu Chen-pu to visit Japan is a grave event in China-Japan relations," said a statement from China's Foreign Ministry.

"Chinese mainland strongly protests the move, which goes against the three Sino-Japanese political documents and related promises," the statement said.

Reports said Hu, who assumed the top post in Taiwan's army in February, arrived in Japan as an "ordinary tourist" on Tuesday, and watched one of the Japanese Ground Self-Defense Force's major live-fire drills conducted Thursday in Shizuoka Prefecture.

"We strongly demand the Japanese government demonstrate its one-China policy with concrete acts and earnestly treat China's solemn stance and grave concerns so as to prevent similar events from happening again," the statement said.