SEOUL, South Korea — President Moon Jae-in of South Korea called on Thursday for family reunions for older Koreans separated by war six decades ago in a conciliatory move after the North’s first test of an intercontinental ballistic missile.

Mr. Moon, a dogged advocate of dialogue with the North, made the proposal during an address in Germany, where he was scheduled to attend a Group of 20 summit meeting this week. In his first speech since North Korea’s missile test on Tuesday, Mr. Moon reaffirmed his policy of seeking to engage the North through negotiations even as his government vowed to join Washington in tightening sanctions against the North after its ICBM test.

“What the North chose to do this time was reckless,” Mr. Moon said in a speech delivered at the Körber Foundation, a nonprofit research group based in Berlin. “It asked for punishment from the international community.”

He added, “If the North doesn’t stop its nuclear pursuit, there is no other option but to enforce even stronger sanctions and pressure.”