Prime minister Shinzo Abe sparked anger on Thursday by saying there was "no evidence to prove there was coercion".

South Korean foreign minister Song Min-soon said his remarks were "not helpful" and the truth must be faced.

Historians believe at least 200,000 women were forced to serve in Japanese army brothels during World War II.

A Japanese cabinet spokesman appeared to play down Abe's comments by saying the prime minister stood by a 1993 government apology for the use of so-called "comfort women".

But Song said the Japanese leader's remarks were not helpful in efforts to build better relations between the two countries.

"There has been debate over the question of whether there was coercion, " Abe told journalists on Thursday. "But the fact is, there was no evidence to prove there was coercion as initially suggested."

The US congress is considering a resolution calling on Tokyo to "formally acknowledge, apologise and accept historical responsibility" for the coercion.

The draft text was debated by the House of Representatives last week, prompting criticism from Japan's foreign minister, who said it was "not based on objective facts".

Some Japanese conservative politicians have questioned the extent of the country's wartime atrocities. A number are seeking to downgrade the government's 1993 acknowledgement that the Imperial Army ran brothels for its troops during the war.

The non-binding resolution before the US congress seeks to reject the revisionists' moves.

Three former comfort women gave evidence at the US hearing, describing the rape and torture they endured at the hands of Japanese soldiers.