South Korean President Park Geun-Hye called Thursday for the first family reunions with North Korea in three years, a day after the two nations agreed to reopen a joint industrial zone.

In a speech marking the anniversary of Korea's liberation from Japanese rule in 1945, Park urged Pyongyang to "open its heart" and agree to a meeting next month for families left divided for decades by the Korean War.

The South Korean leader also welcomed Wednesday's agreement on the Kaesong industrial park, which she said could start "inter-Korea relations anew" after months of sky-high tensions.

Separately, police fired a water cannon to break up a protest in central Seoul calling for better relations with North Korea, Yonhap news agency said. Some 140 students meanwhile were detained by police over another rally, itreported.

"I hope that the North will open its heart so that the divided families can be reunited around the Chuseok holiday," Park said, referring to a traditional Korean harvest festival that this year falls on September 19.

Millions of Koreans were left separated by the 1950-53 war. The last round of reunions to allow ageing relatives to meet for a few days under Red Cross auspices took place in 2010, when as in previous rounds there were scenes of high emotion.

About 72,000 South Koreans -- nearly half of them aged over 80 -- are still alive and waiting for a chance to join the highly competitive family reunion events, which select only up to a few hundred participants each time.

South Koreans are allowed only in very rare circumstances to cross the heavily militarised border.

"I have so much hope this time," Song Il-Whan, a 77-year-old who was separated from his two siblings when he was 14, told Yonhap.

"Look how old I am now... I really wish I could meet them this time," said Song, adding he had been applying for the family reunion programme for the past 15 years with no success.

North Korea last month proposed holding talks on resuming the family reunion programme in conjunction with discussions about the Kaesong industrial complex. But it retracted the offer after Seoul insisted that the two issues should be dealt with separately.

The Seoul-invested industrial zone, built just north of the border in 2004 as a rare symbol of cooperation, ground to a halt in April after remaining immune to cross-border political swings for years.

Pyongyang, angered at a joint South-US army drill coming after it conducted a nuclear test in February, withdrew all its 53,000 workers from Kaesong. Seoul soon pulled out all its company managers.

Six previous rounds of talks since April had foundered on the South's insistence that the North take full responsibility for the crisis and provide a binding guarantee that it would not close the complex again. Pyongyang had refused to do so.

But Wednesday's agreement suggested a compromise in which the North accepted the worker pullout had closed Kaesong, while both sides promised jointly to ensure the zone remained open in the future.

However, the two sides failed to set a precise date for the resumption of operations at Kaesong, and the South sounded a note of caution after the deal was announced.

"This agreement is not an end but only a beginning," its chief negotiator Kim Ki-Woong told reporters.

Still, the agreement drew support from the US and UN chief Ban Ki-moon, and analysts said it should clear the way for cooperation in other fields, despite North Korea's warnings against the latest set of US-South Korea drills starting next Monday.

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