North Korea nuclear test was 10 times bigger than Hiroshima blast, U.S. says

North Korea's most recent nuclear test produced an explosion almost 10 times larger than the blast from the bomb dropped over Hiroshima in 1945, U.S. officials tell CBS News' David Martin.

The initial U.S. intelligence assessment of Sunday's test indicates the underground explosion measured 140 kilotons. The Hiroshima explosion yielded a blast of 15 kilotons. One kiloton is equivalent to the force produced in an explosion of 1,000 tons of TNT.

North Korea says Sunday's explosion came from a hydrogen bomb capable of fitting on an intercontinental ballistic missile (ICBM), which would represent a significant advance in its nuclear program. Hydrogen bombs are much more powerful than atomic bombs, like those dropped on Hiroshima and Nagasaki. U.S. intelligence officials have not determined whether Sunday's test was the result of a hydrogen bomb.

The explosion was North Korea's sixth nuclear test since 2006 and its largest yet. The U.S. Geological Survey said the blast registered as a magnitude 6.3 earthquake. Satellite imagery showed numerous landslides around the test site, according to an analysis by John Hopkins University's 38 North.

The test set off yet another round of condemnation in the region and around the world. During an emergency meeting of the U.N. Security Council on Monday, U.S. Ambassador Nikki Haley said North Korea was "begging for war" and called for tougher sanctions against the Kim Jong Un regime.

Asked about the possible use of military force against North Korea, President Trump said Wednesday that military action is "not our first choice." Mr. Trump spoke with Chinese President Xi Jinping earlier in the morning, and said Xi "would like to do something" about North Korea. 

"We'll see whether or not he can do it," Mr. Trump said.

In South Korea, U.S. forces are in the process of installing the last four missile launchers in its controversial missile defense system. The Terminal High Altitude Area Defense system, or THAAD, has been seen by some in the region and South Korea as a provocative measure that exacerbates tensions with the North. 

In a phone call Friday, Mr. Trump and South Korean President Moon Jae-in reached an agreement that will allow Seoul to increase the explosive power of its missiles and to buy billions more in U.S.-made weapons.