TOKYO, Jan. 12 (Xinhua) -- Japanese Prime Minister Shinzo Abe on Friday rejected South Korea's calls for a sincere apology to the "comfort women" who were forcibly conscripted to work in wartime military brothels, despite evident flaws in a bilateral deal.

Abe's remarks, the first from the Japanese leader since South Korean President Moon Jae-in called for the apology during a recent New Year's press conference, came despite Seoul not requesting a bilateral deal on the issue be renegotiated.

"We can by no means accept South Korea's unilateral request for additional measures. The Japan-South Korea deal was a promise between countries. It is an international and universal principle to keep it," Abe told reporters prior to departing for an Eastern European tour.

Moon had stated that while it is "undeniable" that the deal is an official bilateral agreement, the "erroneous knot" with Japan over the "comfort women" issue must be untied by Tokyo apologizing to the victims.

Under a landmark bilateral deal struck in December 2015 under the government of Moon's predecessor Park Geun-hye, both countries agreed that the "comfort women" issue, that had significantly strained diplomatic ties between both countries, would be "finally and irreversibly" resolved.

However, Moon said in December that the wartime sexual slavery issue cannot be resolved by the 2015 deal with Japan as a secret agreement was found between the two countries after reviewing the procedure of the deal.

Moon said at the time that a grave fault was found in procedures and content of the 2015 negotiations between the two governments that proved to be a costly blunder.