TOKYO -- A diplomatic furore over Japan's wartime brothels looked unlikely to fade after Tokyo said on Friday a 14-year-old study had found no evidence the government or military officials had kidnapped women to act as prostitutes.

Prime Minister Shinzo Abe's latest statement -- which was issued in response to an opposition lawmaker's query and which also reiterated that Japan stood by a 1993 apology -- came as the U.S. ambassador to Japan said he believed the women were forced to act as sex slaves for Japanese soldiers during World War Two.

"I take the word of the women that testified," U.S. envoy Thomas Schieffer told a group of journalists. Three former sex slaves testified to U.S. Congress last month.

"I think that they were coerced to engage in prostitution ... That means they were raped by Japanese military at that point in time," he added. "I think that happened and I think it was a regrettable, terrible thing that it happened.

"I think the events speak for themselves."