Defence Secretary Sir Michael Fallon has said Britain will not "step back" from European defence despite its impending withdrawal from the EU.
Sir Michael, in Washington for talks with his US counterpart General James Mattis, will reaffirm the UK's commitment to bolstering "Euro-Atlantic security" through the Nato alliance.
"Today our nations are facing a wave of multiple, concurrent, diverse global threats: from Islamist extremism, Russian state aggression, from sponsors of terror, from North Korea testing nuclear bombs and firing off missiles, from the insidious spread of misinformation and from Wannacry-like cyber attacks," he will say.
"Such events demand an international response, so we see Brexit as an opportunity not to step back from European defence but to step up to strengthen Euro-Atlantic security. In particular, we're bolstering our bonds with Nato - the cornerstone of defence."
His comments came as US President Donald Trump finally confirmed his commitment to Nato's Article 5 – which says an attack on one member state is an attack on all.
In a speech in Poland on Thursday ahead of the G20 summit in Hamburg, Mr Trump said the US had "demonstrated not merely with words, but with its actions" that it stood firmly behind Article 5, "the mutual defence commitment".
Mr Trump - who was highly critical of Nato during the US presidential election campaign - was criticised for failing to explicitly affirm his commitment to the mutual defence of alliance members when he attended a summit at Nato headquarters in Brussels in May.