The United Nations Security Council (UNSC) will hold an emergency meeting today in New York after North Korea claimed it had carried out a "successful" hydrogen bomb test, diplomats said.
The closed-door morning talks between the 15 member nations were called by the United Nations and Japan.
"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.
A hydrogen, or thermonuclear device, uses fusion in a chain reaction.
If North Korea's claim is confirmed, it would massively raise the stakes around its banned nuclear program and likely trigger tougher international sanctions.
Pyongyang has carried out three previous nuclear tests -- in 2006, 2009 and 2013 -- which led to a series of sanctions from the United Nations.
Several UN resolutions ban the reclusive North from any nuclear activity or ballistic missile technology.
At the council, Pyongyang ally Beijing regularly tries to shield the North from condemnation or sanctions, while Washington repeatedly denounces the communist regime and its human rights violations.
Japan joined the council on January 1 under a two-year mandate as a non-permanent member.