North Korea’s H-bomb test today presents a serious dilemma for world leaders and the United Nations Security Council is holding an emergency meeting today in New York.

"While we cannot confirm at this time that a test was carried out, we condemn any violation of UNSC Resolutions and again call on North Korea to abide by its international obligations and commitments," US mission spokeswoman Hagar Chemali said.

If the test was indeed a hydrogen bomb, it would mark a significant increase in capabilities from the North, which previously tested far less fission blasts generated by uranium or plutonium.

If North Korea's claim is confirmed, it would massively raise the stakes around its banned nuclear program and likely trigger tougher international sanctions.

The US said it could take days to confirm whether North Korea successfully tested a hydrogen bomb.

A hydrogen, or thermonuclear bomb, uses fusion in a chain reaction that results in a far more powerful explosion than the fission blast generated by uranium or plutonium alone. 

The H-bomb is thousands of times more powerful than an atomic bomb. While the world has seen the horror of 15 to 20 kiloton atomic bombs dropped on Japan, the only known test of dry hydrogen bomb by the US produced a yield of 15 megatons.

Here's why: In order to combine the small atoms and start a fusion reaction, such a bomb needs a large amount of energy. And that energy comes from an atomic bomb inside the hydrogen bomb. A hydrogen bomb causes two separate explosions and hence is also known as thermonuclear bomb.

Initial reports said an earthquake measuring a 5.1 magnitude was registered in North Korea near a known testing site in the isolated country. It is called the Punggye-ri Nuclear Test Site, which is in the Kilju County, North Hamgyong Province. This is the same site where the alleged 2006, 2009 and 2013 nuclear bomb tests took place.