Prime Minister Shinzo Abe and South Korean Prime Minister Lee Nak-yeon agreed Tuesday to work together toward the denuclearization of North Korea, before the third inter-Korean summit next week.

“I would like to express my respect to your country’s persistent efforts seeking to improve South and North Korean ties and bridge between the United States and the North,” Abe said at the outset of the meeting in Vladivostok, which was held on the sidelines of a regional economic forum.

Abe also stressed the necessity of promoting their bilateral and trilateral cooperation involving Washington in dealing with Pyongyang.

In response to Abe’s comments, Lee said, “South Korea has never forgotten the necessity of cooperation with the international community, including the United States and Japan, in realizing the denuclearization and peace of the Korean Peninsula.”

South Korean President Moon Jae-in and the North’s leader Kim Jong Un will meet in Pyongyang from Sept. 18-20, as the United States and North Korea have reached an impasse in their negotiations on the North’s nuclear program since the historic summit between U.S. President Donald Trump and Kim in June.

Abe and Lee also reaffirmed the importance of their bilateral ties. This year marks the 20th anniversary of a joint declaration seeking to promote future-oriented relations, which was agreed on by then Prime Minister Keizo Obuchi and South Korean President Kim Dae-jung.

They also took up the issue of “comfort women,” Japan’s Foreign Ministry said, referring to the women and girls forced to provide sex for Japanese troops in military brothels before and during World War II — a thorny topic between the two neighbors.

The ministry said Abe told Lee that Japan’s stance remains unchanged in seeking to implement a 2015 landmark bilateral accord aimed at “finally and irreversibly” resolving the decadeslong issue. The ministry declined to provide Lee’s response to the comments by Abe.

The bilateral agreement included a provision that Japan provide South Korea with a ¥1 billion ($9 million) fund to settle the matter. But Moon’s government has said the deal, agreed under his predecessor Park Geun-hye, does not fully address the issue and has urged Japan to take additional steps.

Moon did not attend the Eastern Economic Forum despite Moscow inviting him to the Russian Far East port city.

The forum has been held since 2015 under Putin’s initiative to attract investment to the region.