The United States would like to see "a very strong United Kingdom staying in a strong EU", secretary of state John Kerry has said.
Mr Kerry said it was "profoundly" in America's interests that the UK voted to remain in the union in the upcoming referendum.
David Cameron's renegotiation drive is approaching its moment of truth at a Brussels summit next week.
Speaking at a security conference in Munich, Mr Kerry said: "I want to express the confidence of President Obama and all of us in America that, just as it has so many times before, Europe is going to emerge stronger than ever, provided it stays united and builds common responses to these challenges.
"Now obviously, the United States has a profound interest in your success as we do in a very strong United Kingdom staying in a strong EU."
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HMRC has told MPs it wanted to fine Google over their tax affairs - but could not prove their accounts were assembled with "insufficient care".
Earlier Google finance boss Tom Hutchinson said HMRC determined they had a "reasonable argument" for the amount of UK profit they declared.
"And that's why there was no penalty," he added.
Google has insisted the £130 million UK tax deal with HMRC is "fair".
The company's finance boss Tom Hutchinson said the figure was the largest tax settlement following an audit ever paid by Google outside the US.
He added the firm had not incurred any fines because HMRC determined they had a "reasonable argument" for the amount of profit they were showing.
"HMRC looks and sees, are we just ignoring the rules? Or did we interpret the rules in a reasonable way?" he said.
"And they determined we did, and that's why there was no penalty."
Google bosses were today accused of "living on a different planet" as they were grilled by MPs over their controversial UK tax deal.
Committee chair Meg Hillier asked Google UK boss Matt Brittin: "You're British, you're a British taxpayer. So don't you feel a bit embarrassed by this?
"The fact that you don't even know what you're paid? You're living on a different planet.
"Frankly, you are taxing my patience and the patience of the hard-working taxpayer out there."
Mr Brittin said: "I'm proud to be British. I appear here because I believe in the process of democracy."
But he insisted Google were paying the right tax in the UK: "It's not 3%, it is 20%."
Google's finance boss Tom Hutchinson added the £130 million deal was "fair" and said it was the biggest settlement they had agreed outside the US.
The UK boss of Google claims he "does not know how much he gets paid" as he was grilled by MPs today.
Matt Brittin said he "understood the anger and frustration" of UK taxpayers over his company's £130 million tax deal with HMRC.
But Public Accounts Committee chair Meg Hillier hit back: "Do you really understand the anger Mr Brittin? What do you get paid?"
Mr Brittin repeatedly dodged the question saying: "I don't have the exact figure" and would provide it to the committee "privately, if it was relevant".
When pressed further, Ms Hillier said: "My point is, taxpayers out there, our constituents, are very angry.
"They live in a different world to you, clearly, if you can't even tell us what you actually get paid. I wonder if you've got tin ears."
Earlier the committee heard Google's Chief Executive was paid £138 million in the last year alone.
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