Japan must squarely face up to its “unbeautiful” past and learn lessons from its wartime aggression if it wants to ensure smooth cooperation with South Korea and China, Chinese Foreign Minister Wang Yi said Tuesday, ahead of a trilateral summit among the three nations in Seoul.

President Park Geun-hye will host Chinese Premier Li Keqiang and Japanese Prime Minister Shinzo Abe over the weekend for the three-way summit that had been on hold since 2012 due to a bitter territorial dispute between China and Japan, as well as Japan’s unrepentant attitude over its wartime past.

Speaking at a forum on public diplomacy among South Korea, China and Japan, Wang said cooperation among the three nations has been significantly undermined because of Japan’s “retrogression toward history.”

“If the issue of history is properly dealt with, cooperation among the three nations will move forward. If not, it will be inevitably halted,” Wang said.

“We hope that the Japanese side can sincerely reflect upon all its past mistakes, directly make a clean break with its unbeautiful past, and take an entirely new approach to join hands with the people of China and South Korea,” Wang said.

South Korea, China and Japan last held a trilateral summit in May 2012. The annual event has been stalled since then, mainly due to a then-simmering territorial dispute between China and Japan, as well as Japan’s lack of apologies over its atrocities during World War II.

The upcoming trilateral summit paved the way for Park to hold her first one-on-one meeting with Abe. South Korean officials said Seoul has offered to hold a bilateral summit between Park and Abe on next Monday.

Park and Abe have not held a one-on-one meeting since they took office about three years ago and one of the big obstacles is Abe’s lack of apology for the sexual enslavement of Korean women by the Japanese military during World War II.

Park has said she was open to holding a bilateral summit with Abe, but stressed that Japan must make progress in its efforts to resolve a long-standing grievance regarding the former sex slaves.

Historians estimate that more than 200,000 women, mostly Korean, were coerced into sexual servitude at front-line Japanese brothels during the war. From 1910 to 1945, the Korean Peninsula was a Japanese colony.