A test of a hydrogen nuclear bomb by North Korea would be a "grave breach of UN Security Council resolutions", British Foreign Secretary Philip Hammond has said.
Hammond, who is on a two-day trip to Beijing, said if the reports were true he condemned the provocation "without reservation."
If North Korean H-bomb test reports are true, it is a grave breach of #UNSC resolutions & a provocation which I condemn without reservation
A US military statement said the low-level flight over ally South Korea was in response to the North's 'recent provocative action'.
Tens of thousands of people danced and applauded in central Pyongyang, North Korea, in support of the country's reported H-bomb test.
Why is this latest development in North Korea's quest for nuclear power seen as potentially significant?