Move highlights differences between Seoul and Washington over how to deal with Pyongyang.

North and South Korean officials tested a special hotline for the first time in almost two years Wednesday, signaling a tentative thaw on the divided peninsula and highlighting differences between Seoul and Washington over how to deal with a nuclear-armed Pyongyang. The reactivation of the telephone link across the demilitarized zone—severed by the North in 2016—came as South Korea’s government moved swiftly to follow-up on a New Year’s Day suggestion by North Korean leader Kim Jong Un that he would be open to talks. The North dialed the South and the call lasted about 20 minutes, according to the South’s unification ministry. “Hello, this is [name] speaking,” were the first words from a North Korean official on the line, according to the ministry, which didn’t release the North Korean official’s name or a full transcript.

The tenor of the South’s diplomatic outreach offered a stark contrast to the tone from Washington, where President Donald Trump tweeted that he had a “Nuclear Button” that “is a much bigger & more powerful one” than one Mr. Kim boasted about in a New Year’s Day speech.

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