North Korea claims it successfully conducted a test of a hydrogen bomb Sunday--meant for an intercontinental ballistic missile.

The United Nations Security Council is holding an emergency meeting on Monday in response to the test.

This is North Korea's sixth nuclear test since 2006 and its most powerful.

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"It'll take a few days for us to get exact estimates for how large and how powerful this test was but all the indications are that this was a substantially more powerful test than North Korea has previously conducted. Probably a two-stage thermonuclear weapon. So a much more powerful device than they've previously demonstrated," said Mark Bell, an assistant professor at the University of Minnesota's Department of Political Science.

Bell's research looks at issues related to international security, causes of war, U.S. foreign policy and particularly things having to do with nuclear proliferation and nuclear strategy.

"This is clearly a bigger and more sophisticated nuclear weapon that North Korea has tested. I think it's part of a general strategy... on the North Korean side of trying to demonstrate that they clearly have the ability to deliver a nuclear weapon, a powerful nuclear weapon, to the cities of the United States," Bell said.

When leaving St. John's Episcopal Church on Sunday, a reporter asked President Donald Trump if he would attack North Korea, which the president responded to with, "We'll see."

President Trump also tweeted, "North Korea has conducted a major Nuclear Test. Their words and actions continue to be very hostile and dangerous to the United States..." He went on to tweet, "South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"

Defense Secretary Jim Mattis told reporters after meeting with the president, "We have many military options and the president wanted to be briefed on each one of them. We made clear that we have the ability to defend ourselves, our allies--South Korea and Japan--from any attack. And our commitment among the allies are ironclad."

Mattis also said, "We are not looking to the total annihilation of a country, namely North Korea. But, as I said, we have many options to do so."

President Trump also tweeted that the United States is considering, among other options, stopping all trade with any country doing business with North Korea.