Theresa May has told Japan that the UK will stand “shoulder to shoulder” with them over the threat from North Korea.
The prime minister is in Tokyo where she will announce increase in mutual cooperation over defence and cyber-security.
“The prime minister told Prime Minister Abe that the UK stood shoulder to shoulder with Japan in facing North Korean aggression,” the spokeswoman said.
“The prime minister also discussed the importance of the show of unity at the UN security council last night in speaking with one voice against North Korean aggression.
She added: “Prime Minister Abe and the prime minister agreed that it was important to send a powerful message to North Korea that it won’t be tolerated.”
“As two outward-facing countries with many shared priorities and shared challenges, Japan remains a natural partner for us on defence and security issues.
I am determined that our defence and security co-operation will continue to go from strength to strength, enhancing our collective response to threats to the international order and to global peace and security, through increased co-operation on defence, cyber security, and counter-terrorism.
And that must include confronting the threat that North Korea poses and ensuring the regime stops its aggressive acts.”
This comes after Nuclear-armed North Korea fired a ballistic missile over Japan and into the Pacific Ocean in what is being called a major escalation.
The missile was launched at around 2057 GMT Monday from Sunan, near Pyongyang, travelling over Japan.It flew around 2,700 kilometres (1,700 miles) at a maximum altitude of around 550 kilometres.
No effort was made by Japan to intercept the missile but a warning was issued warning telling citizens in Hokkaido to seek shelter.
Foreign Secretary Boris Johnson said Britain was working with the United States and allies in the region to find a diplomatic solution to the stand-off between Pyongyang and Washington and that “the North Korean regime is the cause of this problem and they must fix it.”
First Secretary of State Damian Green has also added it is “obviously” in Britain’s interests that the stand-off between Washington and Pyongyang does not lead to conflict and urged Mr Trump to be “sensible” and go through the UN before acting on his “fire and fury” threat.