SEOUL, South Korea — South Korea's president called on Monday for resuming reunions of families separated by war, expressing hopes that the humanitarian program would improve strained ties between the rival Koreas.

The call comes amid lingering tensions on the Korean Peninsula following Pyongyang's fiery rhetoric and threats of nuclear wars last spring. The two Koreas had planned to hold family reunions in September for the first time in three years but Pyongyang cancelled them at the last minute.

President Park Geun-hye told a televised news conference that she wants the reunions to take place on the occasion of the Lunar New Year's Day later this month to "heal wounded hearts."

She said she hopes the two Koreas would find a new momentum for better ties with the reunions. She said her government plans to expand civilian exchanges with North Korea and approve the shipments of more humanitarian assistance to North Korea.

Millions of people have been separated since an armistice that ended the 1950-53 Korean War has never been changed to a peace treaty. The reunions are highly emotional as most applicants are in their 70s or older and are eager to see their loved ones before they die. The two Koreas bar ordinary citizens from exchanging letters, phone calls or email.

North Korean leader Kim Jong Un last week called for improved ties in his New Year's Day speech that included a warning of a nuclear war. South Korean officials responded by saying North Korea must first take nuclear disarmament steps and questioned the sincerity of Kim's overture.

North Korea issued similar conciliatory gestures in its New Year's Day message last year before it conducted its third nuclear test in February and made a torrent of threats to launch nuclear strikes against Seoul and Washington in the spring.

Park said that North Korea should act with sincerity. "Last year, North Korea talked about improvement in South-North Korean ties in its New Year's Day message but you know very well how it acted in reality," she said.

Yoo Ho-Yeol, a professor of North Korea studies at Korea University in South Korea, said the family reunions are a "litmus test" for improved ties between the two Koreas. He said the reunions, if realized, can lead to the resumption of other stalled inter-Korean cooperation projects.

Worries about North Korea have deepened after the execution of leader Kim's once-powerful uncle Jang Song Thaek on treason charges last month, with Seoul officials saying Pyongyang may launch provocation to create tension to bolster internal unity.

Park said North Korea has become "more unpredictable" following Jang's execution and that South Korea will study and brace for any possible scenarios.

She reiterated her position that she can meet Kim anytime if it's necessary for promoting peace on the peninsula but talks must not be held for talks' sake.