Pentagon chief James Mattis says any threat to the US or its allies from North Korea will be met with a "massive military response".
These comments come after the national security meeting with US President Donald Trump.
Penian says it has successfully tested a more advanced nuclear weapon - a hydrogen bomb.
North Korea has defied UN sanctions and international pressure to conduct nuclear weapons tests that could reach the US.
But, speaking to reporters outside the White House, Mattis said that the US has the ability to defend itself and its allies such as South Korea and Japan, reports KosovaPress.
"Any threat to the United States or its territories — including Guam — or our allies will be met with a massive, effective and massive military response," Mattis said.
