The head of Nato is appealing to Western allies to continue to work together in the interests of shared security, despite a series of public rifts between the US and other member states.
In a speech in London on Thursday, Nato Secretary General Jens Stoltenberg will say that while there are real differences among alliance members, they should not be allowed to undermine the transatlantic bond.
His warning comes amid reports Donald Trump is preparing to meet Russian president Vladimir Putin during his forthcoming visit to Europe.
If it goes ahead it would be another blow to Western unity after a bruising G7 which laid bare divisions between the US administration and European and Canadian allies across a range of issues including trade and the Iran nuclear deal.
It would also be a further setback for Theresa May in her efforts to isolate Russia diplomatically over the Salisbury nerve agent attack on Sergei Skripal and his daughter, Yulia, which Britain blames on the Kremlin.
The US president caused consternation at the G7 summit in Quebec earlier this month when he suggested Russia, which was expelled from the grouping in over the annexation of Crimea in 2014, should be readmitted.
The Times quoted senior UK Government sources as saying US officials were now looking to fix a meeting with Mr Putin either before the Nato summit in Brussels on July 11 or after Mr Trump’s visit to the UK on July 13.
The report comes as Downing Street was forced to deny claims that the Prime Minister had cast doubt on Britain’s continuing status as a “tier one” military power.
The Financial Times reported she had sent “shock waves” through the Ministry of Defence after telling Defence Secretary Gavin Williamson he needed to rethink which capabilities the UK needed for a modern military force.
A No 10 spokesman said: “The Prime Minister is strongly committed to the United Kingdom’s armed forces and to maintaining their strength and their ability to deter and where necessary defeat the threats we face.
“It is categorically untrue to suggest otherwise or that the UK’s position as a tier-one defence nation is somehow in question.”
With many of the participants at the G7 due at the Nato meeting, there are fears in European capitals that it will become the stage for another transatlantic diplomatic bust-up.
Since the G7, Mr Trump has since publicly taunted German Chancellor Angela Merkel over migration while demanding the Europeans contribute more to the costs of their common defence.
The US president has in turn faced criticism over the separation of children from parents detained as illegal immigrants on the US border with Mexico, a practice Theresa May described as “wrong” and “deeply disturbing”.
On Wednesday he signed an executive order allowing families to stay together.
In his speech, Mr Stoltenberg, who is due to meet Mrs May in Downing Street, will argue that maintaining the transatlantic partnership is in the “strategic interest” of all the allies.
He is expected to say: “The lesson of history is that we have been able to overcome our differences.
“Again and again, we unite around our common goal. We stand together. We protect each other.”
In the Commons on Wednesday, Mr Williamson warned that the US could not be expected to pick up the bill for the defence of Europe indefinitely.
While Britain met the Nato target of spending a minimum of 2% of GDP on defence, he said that other allies needed to do more.
“We can’t continue to expect US taxpayers to keep picking up the tab for European defence indefinitely, nor can we expect US patience to last forever.
“We as a continent have to step up to responsibility of playing a pivotal role in defending ourselves and not to expect others to do it for us.”