The United States warned Japan in March that Washington could no longer back Tokyo on the issue of North Korea's past abductions of Japanese unless then Prime Minister Shinzo Abe reversed his contentious claim that there was no proof that the Imperial forces forced women and girls into sexual slavery during the war, sources revealed Thursday.

The warning, delivered by U.S. Ambassador Thomas Schieffer to a senior government official, prompted Abe to change his stance and announce that he stands by Japan's 1993 official statement of apology to the "comfort women," as they are euphemistically known, the sources said.

The 1993 statement, issued by then Chief Cabinet Secretary Yohei Kono, acknowledges and apologizes for the Imperial forces' involvement in forcing women and girls to work in frontline brothels in Japanese-occupied areas in the 1930s and 1940s.