Britain and the US are to step up calls for other Nato member states to meet the alliance's target on defence spending to counter Russian aggression and the threat of terrorism.
Defence Secretary Sir Michael Fallon will join his US counterpart Jim Mattis in insisting more allies must move towards the target of spending 2% of GDP on defence, when they meet for talks in London.
Their message will be underlined by Foreign Secretary Boris Johnson at a meeting of Nato foreign ministers in Brussels.
Since assuming office in January, the US administration of President Donald Trump has been pressing European members to take on a greater share of the burden of collective defence.
Britain and the US are among five of the 28 members of the alliance that meet the 2% target.
The meeting comes as The Times reported the armed forces are facing a £10 billion funding shortfall over the next 10 years.
The paper said it had been told by seven serving and former officers that the UK will be unable to meet its military commitments unless the Government addresses the issue.
The Ministry of Defence said it was unclear how the reported shortfall had been calculated.
"Spending is monitored continually to ensure the £35 billion defence budget focuses on frontline priorities and delivers value for money by maximising efficiencies," a spokesman said.
At their talks, Sir Michael and Mr Mattis will discuss measures to modernise Nato, including streamlining the command structure, as well as progress on a series of joint equipment projects including the F-35 Lightning joint strike fighter.
Sir Michael is due to announce £90 million investment at RAF Marham in Norfolk to support Britain's consignment of the new aircraft.
Ahead of the talks, Sir Michael said: "Our defence relationship with the US is unprecedented in its depth and scope.
"As we leave the EU, our bilateral relationships matter more than ever, so we'll be enhancing our co-operation and investing more in our joint F-35 fast jet programme.
"Together we will also agree further steps to modernise Nato and ensure greater burden-sharing.
"That means more European members committing to annual increases in their defence spending in order to counter an aggressive Russia and tackle terrorism and cyber threats."