Democratic U.S. vice presidential candidate Tim Kaine said Tuesday that he would back pre-emptive strikes against North Korea if the isolated nation showed signs of launching a nuclear-tipped missile capable of hitting the United States.

Kaine made the comments in response to a question during the first and only vice presidential television debate in which he faced off with his Republican counterpart, Indiana Gov. Mike Pence.

The two were asked whether they would take pre-emptive action if intelligence showed North Korea was about to launch a nuclear-armed missile capable of reaching the United States.

“Look — a president should take action to defend the United States against imminent threat. You have to. A president has to do that,” Kaine said. “Exactly what action you have to determine — what your intelligence was, how certain you were of that intelligence — but you would have to take action.”

Pence called for a more muscular approach to the North and other threats, saying that the U.S. should rebuild its military, including modernizing its nuclear forces.

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“When Donald Trump is president of the United States, we are not going to have the kind of posture in the world that has Russia invading Crimea and Ukraine, that has Chinese building new islands in the South China Sea, that has literally the world — including North Korea — flouting American power,” he said.

“We are going to go back to the days of peace through strength,” he added.

Pyongyang sparked international condemnation last month when it conducted its fifth and most powerful nuclear test. North Korean state media has slammed talk in South Korea of a possible strike on the country.

“If the aggressors and provocateurs dare mount a pre-emptive attack on the DPRK, they will not be able to escape a merciless, nuclear retaliatory strike of justice,” the state-run Rodong Sinmun said Wednesday.

The DPRK is the acronym for the North’s official name, the Democratic People’s Republic of Korea.