Claims by North Korea that it conducted a hydrogen bomb test will be top priority in talks in Tokyo between Cabinet ministers and their Japanese counterparts.
Foreign Secretary Philip Hammond hailed Japan as Britain's "closest security partner in Asia" as he arrived in the capital for discussions on security.
Kim Jong-un's secretive state said it successfully tested a miniaturised hydrogen bomb, a move that would be a significant advancement of its nuclear armoury, but experts have cast doubt on the claims.
Mr Hammond will discuss global security challenges with Japanese foreign minister Fumio Kishida alongside Defence Secretary Michael Fallon and his opposite number Gen Nakatani.
The Foreign Secretary, who arrived in the country after visits to China and the Philippines, will also meet Prime Minister Shinzo Abe.
"The UK and Japan are close allies. We enjoy a strong, historic relationship, based on common values and support for democracy, the rule of law, human rights and open markets," Mr Hammond said.
"The long-term security of both the UK and Japan depend on upholding a stable international system. We will continue to work closely together to contribute to global prosperity, peace and security.
"The world today is increasingly dangerous, complex and uncertain. We face growing threats from terrorism and extremism, a resurgence in state-based threats including nuclear proliferation, and an escalation in challenges to our cyber security and to the rules-based international order. It is more important than ever for the UK to work with allies like Japan to counter these threats.
"As a permanent member of the UN Security Council, the UK is continuing to play a central role on the issues that matter and is working with allies like Japan to safeguard national security, as well as building our prosperity overseas."