Japan's ambassador to the U.S. reiterated Wednesday that the passage of a resolution in the U.S. Congress to seek a clear apology from Tokyo over the Japanese military's use of sex slaves during the war would harm bilateral relations.

Ryozo Kato made the statement ahead of the resolution's anticipated passage through a House of Representatives panel next week.

"It is harmful for Japan-U.S. relations if a factually unfounded resolution is passed," he told a news conference, citing the nonbinding resolution authored by Rep. Michael Honda, D-Calif.

"The Japanese government's position on this is as stated by Prime Minister (Shinzo) Abe, when he came to the United States (in April)," Kato said. "That is, we have offered and will offer heartfelt apologies for the hardships incurred by former 'comfort women.' "