South Korean President Yoon Suk Yeol called Friday for the international community to back "unification efforts" after Pyongyang earlier this year declared Seoul its "principal enemy".
Ties between the two Koreas have been in a deep freeze as Pyongyang accelerates its weapons development programmes and Seoul ramps up military cooperation with Washington and Tokyo.
Yoon, who has consistently taken a firm stance against nuclear-armed North Korea, has rarely discussed the topic of unification since assuming office in 2022.
"Our unification efforts must become a source of hope and a beacon of light for the people of North Korea," he said at a ceremony marking the anniversary of Korea's 1919 uprising against Japanese colonial rule.
"We must come together on a path that leads ultimately to unification" of the Korean peninsula, he said, stressing that the international community "must pool its strength in a responsible manner".
Yoon emphasised better ties with Tokyo were helping to counter the North's ever-increasing military threats.
"The security cooperation between the two countries against North Korea's nuclear and missile threats has been strengthened further," he said, adding that the countries were "working together to overcome the painful past".
Last month, the North Korean leader's powerful sister Kim Yo Jong said her country would be open to improving ties with Tokyo, even hinting at a possible future invitation to Pyongyang for Japan's leader.
Her comments came after Kim Jong Un said in December that he would no longer seek reconciliation and reunification with the South, blaming Seoul and Washington for creating an "uncontrollable crisis".
This year, North Korea conducted live-fire drills near the contested maritime border, prompting counter drills by the South and evacuation orders on two islands.
Pyongyang also declared South Korea its "principal enemy" and threatened war over "even 0.001 millimetres" of territorial infringement.
Yoon responded by telling his military to "act first, report later" if provoked by Pyongyang.
In the event of an attack, he said Seoul will hit back "multiple times stronger".
The isolated North has shut agencies dedicated to promoting reunification and fostering communication with Seoul.
"The tyranny and human rights abuses of the North Korean regime deny the universal values of humanity," Yoon said on Friday.
South Korea is gearing up for a crucial election on April 10, with Yoon's conservative party hoping to regain a parliamentary majority for the first time since 2016.
