Japanese experts Tuesday hailed joint celebrations by leaders from South Korea and Japan for the 50th anniversary of diplomatic ties but stressed the need for further efforts to resolve the thorny issue of Tokyo's wartime sex slavery.

President Park Geun-hye and Japanese Prime Minister Shinzo Abe on Monday attended each other's embassy events in their capitals to celebrate half a century of relations, raising hopes that the long-strained relations between the two may improve in the landmark year.

The bilateral ties have been severely frayed due to Japan's denial of its wartime atrocities, such as Tokyo's sexual enslavement of Korean women during Japan's 1910-45 colonial rule of the Korean Peninsula.

Since taking office in 2013, Park has shunned a summit with Abe, calling on Japan to face up to its wartime history.

But in what could be seen as a conciliatory mood, Park voiced hopes Monday that this year will be the first year of opening up a new future together while Abe said that he hopes the two neighboring countries will work hand in hand to chart a new era of relations.

Japanese experts said that they appreciated the two leaders for making efforts to improve the strained ties but stressed that more efforts should be made to resolve the core issue of sex slavery.

"It is regrettable that (Japan) fell short of expressing (more determination) to resolve the sex slave issue," said Haruki Wada, an emeritus professor of Tokyo University.

"But South Korea and Japan have agreed to work together over the issue. ... It is good for the two countries to get to this point. Through consultations, I hope Japan can present an outcome that can satisfy Korean victims of the sex slavery," he added.

Yuki Asaba, a professor at the University of Niigata Prefecture, welcomed the joint celebrations by Park and Abe, saying that their attendance reaffirms their strong political will to improve ties.

"The move was a wealthy welcome. But it still remains to be seen whether this mood can pave the way for a summit between the two leaders," Asaba said.

The professor said that Japan takes heavy responsibility for the sex slave issue, but Seoul should also make efforts to help Japanese people dispel doubts about whether the issue can be clearly resolved.

Kimiya Tadashi, a professor at Tokyo University, said that the two sides should make strenuous efforts to resolve the sex slave matter as it is hard to yield satisfactory results if the two don't make concessions.

Seoul has demanded that Tokyo show sincerity by resolving the sex slave issue in a way that is acceptable to the living victims.

But Japan has long dismissed South Korea's demands, saying that all grievances related to its 1910-1945 colonial rule were settled through a 1965 treaty that normalized bilateral ties. (Yonhap)