SEOUL (Reuters) - South Korean President Moon Jae-in said on Monday ties with Japan are being blocked by historical issues that will take time to resolve and asked for Japan’s understanding on the issue.

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Moon’s comments were an apparent reference to the issue of Korean “comfort women”, a Japanese euphemism for women forced to work in the Japanese military’s wartime brothels.

Any flare-up in the long-running dispute over ‘comfort women’ could complicate efforts by Seoul, Tokyo and their ally Washington to cope with North Korea, which has been ramping up weapons tests since last year in defiance of global sanctions.

Moon told the visiting secretary general of Japan’s ruling Liberal Democratic Party that the people of South Korea did not accept a deal reached by his conservative predecessor and Japanese Prime Minister Shinzo Abe in 2015 to resolve the issue.

But Moon, in his talks with Toshihiro Nikai, apparently did not directly address whether he would try to renegotiate the agreement.

Under the deal, Japan apologized again to the now-elderly women and promised about one billion yen ($9.07 million) for a fund to help them. The two governments agreed the issue would be “irreversibly resolved” if both fulfilled their obligations.

“Both South Korea and Japan should look at this issue directly and understanding is needed that it will take more time (to resolve it),” Moon told Nikai, the South’s presidential office said.

Moon, who suggested during his successful campaign for a May 9 election that he could try to renegotiate the deal, also said the two countries should not “cling to past history” only to block other developments in their ties.

Japanese Chief Cabinet Secretary Yoshihide Suga on Tuesday reiterated that both countries should stick to the agreement.

“This agreement, which is highly evaluated by international society, is being steadily implemented. That is extremely important. We have conveyed this fact to the new South Korean administration through various routes,” Suga told reporters.

Japan wants South Korea to remove a statue near the Japanese consulate in Busan city commemorating Korean comfort women as well as another near the Japanese embassy in Seoul, saying that the presence of the statues violate the 2015 agreement.

Moon on Monday stressed the importance of cooperation with Japan in efforts to denuclearize North Korea and Nikai agreed, the South’s presidential office said, while Suga said the two confirmed the importance of putting pressure on North Korea.

($1 = 110.2200 yen)