The special relationship between Britain and the US "can always be closer", the White House has said.
The statement comes as UK Defence Secretary Sir Michael Fallon talked to US counterpart James Mattis in a "very warm" telephone conversation yesterday.
Sir Michael Fallon said:
"We talked of our joint leadership in NATO, including modernising the Alliance and how we ensure that all members meet the NATO 2% spending commitment alongside America and Britain, with our growing defence budget.
"Operationally, we discussed the importance of working together to accelerate the defeat of current threats, including from Daesh in Iraq and Syria, and tackling terrorism in all its forms.
"I look forward to meeting Secretary Mattis at the next meeting of NATO defence ministers in February."
Donald Trump has said that he is very "excited" about meeting Theresa May in Washington DC on Friday and that they will have a "great conversation" about the potential for trade with the UK, his press secretary Sean Spicer said.
The Prime Minister will become the first foreign leader to meet the new president for talks.
Mr Spicer said the visit, a week after President Trump's inauguration, reflects the historic ties between the UK and the US.
"I think we have always had that special relationship with Britain and that reflects in the Prime Minister's first visit here," Mr Spicer said.
"He's had a great conversation with her and he looks forward to having her here but we can always be closer."
Mrs May will use the meeting to make the case for increasing free trade between Britain and the US.
But Mr Trump has been clear that he believes international trade deals have been damaging for American industry.
Mr Spicer said there would be a "new era of trade policy" that would "put American workers first and foremost".
He added: "We are excited that Prime Minister May is coming on Friday. We look forward to it.
"I'm sure that there will be discussion of trade. The degree to which, I don't know yet. I don't believe we have any plans right now for a joint press conference. That's something that our team will be working out with Prime Minister May. When he talks to Prime Minister May he is going to have a great conversation about the potential for greater trade with the UK."
The Prime Minister will travel to the United States on Thursday when she will become the first foreign serving head of state or government to address the annual congressional Republican retreat, when it gathers for its 30th anniversary in Philadelphia.
In her meeting with President Trump, the PM will stress the "importance of Nato as the bulwark of our defence", following his description of the transatlantic security alliance as "obsolete".
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