Japan's defence minister has revealed North Korea's latest nuclear test was almost twice as big as first thought.
It is estimated to have been around eight times the size of the bomb which destroyed Hiroshima in 1945.
It reportedly shook buildings in China and Russia.
Officials in Seoul put the magnitude at 5.7 while the US Geological Survey said it was a magnitude 6.3.
Measured on the Richter scale, earthquakes which are over magnitude 6 typically only occur globally a little over 100 times per year.
There has been international condemnation of Pyongyang's provocations, but Russia's President says more sanctions are "useless".
The US ambassador to the UN, Nikki Haley, says they are needed.
"Do we think pushing more sanctions on North Korea is going to work? Not necessarily but what does it do? It cuts off the revenue that allows them to build ballistic missiles," said Ms Haley.
US Defence Secretary Jim Mattis reacted to the latest test by saying threats to the United States and its allies "will be met with a massive military response".
Mr Mattis said the United States is "not looking to the total annihilation" of North Korea, but added "we have many options to do so".