Sen. Dan Sullivan (R-Alaska) on Tuesday said President Trump needs Congress to approve a preemptive strike against North Korea.

"[I]f one of the military options that the administration is looking at is a preemptive war on the Korean peninsula launched by the United States, that would require the authorization of Congress," Sullivan said on Fox News's "The Story."

"Article I of the U.S. Constitution is very clear about that," he added.

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Sullivan said if the United States is attacked first, Trump would have more leeway to respond.

"Obviously, as the commander in chief, the president can react to attacks on the country in a way that he has broader authority on that. I was mentioning the discussions of a preemptive war on the peninsula, that clearly goes in the realm of the authorization of Congress."

The Republican lawmaker also praised the Trump administration for including Congress in its diplomatic decisions so far.

"So, right now, the administration's working closely with the Congress. And I think they need to continue to do that, but we’re supportive of their diplomatic efforts right now," he said, pointing to the unanimous United Nations Security Council vote that slapped sanctions on North Korea over the weekend.

Sullivan's comments come at a time of escalating tensions between Washington and Pyongyang.

A North Korean military spokesman reportedly raised the possibility of striking Guam, an American territory, if it felt threatened by the U.S.

The threat of a strike occurred just hours after the president warned that he would unleash “fire and fury” should Pyongyang continue with its threats.

The Washington Post reported earlier in the day that North Korea has successfully produced a miniaturized nuclear warhead that can fit onto a missile, although it is not yet clear whether the nuclear weapon has been tested successfully.

North Korea has repeatedly tested intercontinental ballistic missiles in recent months, with some analysts saying they could reach parts of the U.S.

While it is not new for the state to threaten the U.S. with military action, the further development of its nuclear capabilities has heightened the alarm.

The Security Council's vote to sanction North Korea was in response to missile tests. Sanctions will largely target North Korea's coal, iron, and seafood exports and possibly make the reclusive state suffer a $1 billion financial hit.