South Korea’s president, Moon Jae-in, has vowed to achieve the unification of the Korean peninsula by 2045, a century after the end of the second world war.

In a speech to mark the 74th anniversary on Thursday of Korea’s liberation from Japan’s 1910-45 rule, Moon also said South Korea would “gladly join” hands with its former colonial ruler to defuse an escalating trade dispute whose roots lie in the country’s bitter wartime history.

In Tokyo, Japan’s new emperor, Naruhito, voiced “deep remorse” over the country’s wartime actions, echoing the language used in recent years by his father, Akihito, who abdicated in April.

Moon, a left-leaning liberal who has encouraged dialogue on denuclearisation between North Korea’s leader, Kim Jong-un, and Donald Trump, called on Pyongyang and Washington to arrange a fourth summit between the leaders “at the earliest possible date”.

“This will probably constitute the most critical juncture in the entire process of achieving denuclearisation and establishing peace on the Korean peninsula,” Moon said in a speech at the Independence Hall in the city of Cheonan. “Now is the time for both Koreas and the United States to focus on resuming working-level negotiations … at the earliest possible date.”

Denuclearisation and greater economic cooperation with the North would lay the foundations for lasting peace on the peninsula, he said, vowing to realise unification between North and South by 2045 and to host a joint Seoul-Pyongyang Olympics in 2032.

“A new Korean peninsula, one that will bring peace and prosperity to itself, east Asia and the world, awaits us,” he said.

Moon was speaking soon after Japan’s prime minister, Shinzo Abe, sent a ritual cash offering to Yasukuni, a Shinto shrine in Tokyo that honours 2.5 million Japanese war-dead, including 14 leaders convicted as war criminals.

Abe, a conservative who has said that future generations of Japanese should not have to keep apologising for the mistakes of the past, has visited Yasukuni only once since becoming prime minister in 2012, but has sent ritual offerings during seasonal festivals and on the 15 August anniversary of Japan’s wartime surrender.

There was no immediate reaction from South Korea or China to the gesture.

Emperor Naruhito, who ascended the Chrysanthemum throne in May, said: “Looking back on the long period of postwar peace, reflecting on our past and bearing in mind the feelings of deep remorse, I earnestly hope that the ravages of war will never be repeated.”

Relations between Seoul and Tokyo have deteriorated since South Korean court rulings calling on Japanese companies to compensate Koreans conscripted as forced labourers during the war. Japan, however, insists that all compensation claims were settled under a 1965 treaty normalising bilateral ties.

South Korea, where large anti-Japanese demonstrations were expected to take place on Thursday, has interpreted Tokyo’s recent decision to impose curbs on exports of some high-tech materials as retaliation for the court rulings.

Moon called on Japan to “contemplate” its wartime past, but added: “We hope that Japan will play a leading role together in facilitating peace and prosperity in east Asia while it contemplates a past that brought misfortune to its neighbouring countries.”

Touching on the trade dispute, he added: “If a country weaponises a sector where it has a comparative advantage, the order of peaceful free trade inevitably suffers. A country that accomplished growth first must not kick the ladder away while others are following in its footsteps.

“If Japan better late than never chooses the path of dialogue and cooperation, we will gladly join hands.”