#StrongerIn: Obama UK visit - 'Inside EU better place for Britain to fight terror'

Writing in the Daily Telegraph Obama also said being inside the EU magnifies Britain's influence across the world.

The president arrived for a three-day visit to the UK late on Thursday (21 April).

But writing in the Sun, Vote Leave's Boris Johnson said President Obama's view was "a breathtaking example of the principle do-as-I-say-but-not-as-I-do".

Before meeting David Cameron for talks later, Mr Obama and his wife Michelle will attend a private lunch with the Queen and Duke of Edinburgh at Windsor Castle - the day after the Queen's 90th birthday celebrations.

The Duke and Duchess of Cambridge and Prince Harry have also invited the Obamas to have dinner with them at Kensington Palace on Friday night.

'Silent testament'

The president's intervention in the UK's forthcoming EU referendum on 23 June has been hotly debated and sparked claims of "hypocrisy" from those who want to leave the EU.

However, in his newspaper piece President Obama recognized that ultimately the matter was for British voters to decide for themselves.

But he also said: "...the outcome of your decision is a matter of deep interest to the United States.

"The tens of thousands of Americans who rest in Europe's cemeteries are a silent testament to just how intertwined our prosperity and security truly are.

"And the path you choose now will echo in the prospects of today's generation of Americans as well."