SEOUL — Dozens of elderly South Koreans crossed the heavily fortified border into North Korea on Monday for heart-wrenching meetings with relatives most haven’t seen since they were separated by the turmoil of the Korean War.

The weeklong event at North Korea’s Diamond Mountain resort comes as the rival Koreas boost reconciliation efforts amid a diplomatic push to resolve a standoff over North Korea’s drive for a nuclear weapons program that can reliably target the continental United States.

The temporary reunions are highly emotional because most participants are elderly people eager to see their loved ones once more before they die. Most of their families were driven apart during the 1950-53 Korean War, which ended in a cease-fire, not a peace treaty, leaving the Korean Peninsula still in a technical state of war.

Buses carrying about 90 elderly South Koreans and their family members were moving into the Diamond Mountain resort after crossing into North Korea. Earlier in the morning, the South Koreans, some in wheelchairs and aided by Red Cross workers, had left the buses briefly to enter the South Korean immigration office in the eastern border town of Goseong.

They were to reunite with their long-lost North Korean relatives on Monday afternoon at the start of a three-day reunion.