Britain will support US President-elect Donald Trump's campaign to get Nato countries to spend more on defence, Boris Johnson has said.
In a speech, he said it could not be "justified" that the US accounted for about 70% of Nato defence spending.
He also said the UK would not seek to prevent the EU from forming a closer common defence policy.
During his election campaign, Mr Trump was critical of Nato, describing the Western military alliance as obsolete.
He suggested that the US would think twice about coming to the aid of any Nato ally under attack if it had not paid its "fair share".
'More brutal system'
The UK, which meets the commitment to spend 2% of GDP on defence, has also been urging other countries to increase their contributions.
Mr Johnson, in a speech to the Royal Institute of International Affairs at Chatham House, said the UK must "redouble our resolve to defend and preserve the best of the rules-based international order" to prevent a return to "an older and more brutal system where the strong are free to devour the weak".