SEOUL (REUTERS) - South Korean President Park Geun Hye, thwarted so far in ambitious plans to begin the process of reunifying the Korean peninsula, said the door is open for talks with the North during the upcoming UN General Assembly.

However, Ms Park said in an interview that Pyongyang must show sincerity in seeking a constructive dialogue and "walk the talk" in taking up South Korea's offers for engagement aimed at ending a deadlock after a decade of warming ties.

North Korea will send its foreign minister, Ri Su Yong, to the UN General Assembly meeting, the highest ranking official from the reclusive state to attend in 15 years. Mr Ri's official agenda is not clear.

Pyongyang has not accepted South Korea's overtures and the unpredictable North's official media has heaped insults on Ms Park. Ms Park said there are no current plans to meet North Korean officials in New York. "If the opportunity does arise and they actually have the opportunity to respond and take up our offer, our earlier offer to engage in high level contacts and for dialogue, I think such opportunities would be a good thing," she told Reuters at the presidential Blue House. "If our foreign ministers were also able to engage in dialogue on that particular point, that would also be a good thing," she added.

After 19 months in office, Ms Park has yet to make substantive progress in dealing with Pyongyang, led by the untested 31-year-old Kim Jong Un. The two sides are technically still at war since there was no peace treaty after the 1950-53 Korean War.

North Korea is keeping up its threat to conduct a fresh nuclear device test, which would be its fourth.

Nuclear tests in 2006, 2009 and then in 2013 just as Park was readying to take office brought a wave of U.N. sanctions on the impoverished North, squeezing its arms trade and the source of revenue for a country that exports little else.

- Urges "courageous" decision by Tokyo -

Ms Park also called for a "courageous decision" by Tokyo to improve ties between the two nations. Relations have chilled deeply over the past two years largely over the issue of Korean"comfort women", as those forced to work in Japanese military brothels during World War Two are known.

South Korea maintains that Japan has not sufficiently atoned for the women's suffering and has protested against Tokyo's review of a landmark 1993 apology, which acknowledged the involvement of Japanese authorities in coercing the women.

The government of Japanese Prime Minister Shinzo Abe has said it adheres to the 1993 apology, but that there was no direct documentary evidence that Japanese military or government officials were directly involved in kidnapping the women. "What we wish to see is an apology to these victims as well as a courageous decision on the part of the Japanese political leadership to take measures to wholly restore honour to these comfort women victims. And doing so, I would say, offers a short route to easing the strains in our relationship," Ms Park said.

- Unpredictable and hostile -

Ms Park, who travels on Saturday to Ottawa and then to New York, where she will address the General Assembly, has unveiled an ambitious initiative to engage North Korea to eventually bring the rivals close enough to make unification feasible for most on both sides.

Many in South Korea, especially younger people, support the idea of reunification over the long term but are wary of its economic and social implications.

The 62-year-old Park, Northeast Asia's first female head of state, is the daughter of former President Park Chung Hee, who took power in a military coup in 1961 and led South Korea for 18 years, pulling the country from the wreckage of the Korean War but with an authoritarian hand. He was assassinated in 1979 by his disgruntled intelligence chief.

Uniquely for an incoming South Korean president, Park had held a meeting with a North Korean leader before taking office.

Ms Park visited Pyongyang in 2002 and sat down with then-leader Kim Jong Il to discuss a range of issues affecting the divided Koreas. The North's leader is said to have apologised for a 1968 commando assault on the Blue House while her father was in office.

Kim's son, Jong Un, took over from his father when the elder leader died in December 2011 and has spent the time since then to consolidate his grip on power, having purged and executed his own uncle in what Ms Park described as a "reign of terror".

Ms Park was asked if she thinks the younger Mr Kim is someone she could speak with. "I'm ready to talk with anyone if doing so serves the cause of overcoming the pain of division on the Korean peninsula, and serves the cause of preparing for peaceful unification here. But what's important, I must stress, is not talking for the sake of talking, but rather sincerity and the willingness to walk the talk," she said.

Ms Park highlighted efforts made by her government to reach out to the North, including an offer for high-level officials to meet and improve ties that went into a deep freeze in 2010 with the sinking of a South Korean navy ship, for which Seoul blamed Pyongyang.

After a summit meeting of leaders in 2000, the two Koreas had enjoyed a decade of warming ties, opening the way for commercial exchange and tourism.

Ms Park's plan is first to address humanitarian issues including separated families, then to start helping the North build the economic infrastructure needed for unification, and thirdly to work to narrow the vast gap that has developed between the two peoples over 66 years of division. "We're not actually sitting on our hands waiting for them to act first," Ms Park said. "That's why we made previous proposals and put forward the initiative about peaceful unification and various initiatives that we feel can be readily and immediately put to action by the two sides."