Nato said it was "highly likely" the US president would be at the meeting, although there was no immediate confirmation from the White House.

It is set to be Mr Trump's first appearance in London following Britain's departure from the European Union in March - although on his first trip he avoided spending much time in the capital city while anti-Trump demonstrations were held.

At a Nato summit in Brussels last year Mr Trump demanded that allies commit more to military spending, calling them "delinquent".

By the end of 2020 US allies in Nato will have added an extra $100 billion to its coffers.