David Miliband described the talks as "substantive"
US Secretary of State Hillary Clinton has paid tribute to Britain's "special relationship" with the US, saying it "stands the test of time".
She was speaking after meeting UK counterpart David Miliband, her first ministerial-level talks since President Barack Obama's inauguration last month.
The two discussed Afghanistan, Middle East peace and a range of other issues.
Mrs Clinton also met German Foreign Minister Frank-Walter Steinmeier and said they had covered similar ground.
She told reporters they had spoken about the continued need for German forces in Afghanistan, where Nato is struggling to contain a Taleban-led insurgency.
"As President Obama has made quite clear, we need our closest allies, like Germany, to help us ensure the success and stability of the Afghan nation at this very important moment," she said.
Mrs Clinton described the talks as "an excellent and broad discussion" and Mr Steinmeier's advice on Afghanistan as "constructive".
Mr Miliband was the first foreign minister to meet Mrs Clinton since she began her job two weeks ago.
"Our two countries have stood side by side confronting global challenges for a very long time," Mrs Clinton said at a joint news conference with him.
"We share fundamental values and important fundamental objectives," Mrs Clinton said.
"It's often said that the United States and Great Britain have long enjoyed a special relationship. Well, it's certainly special in my mind and one that has proven very productive.
"Whoever is in the White House, whichever party in our country, this relationship really stands the test of time," Mrs Clinton added.
In his turn, Mr Miliband described the talks in Washington as "substantive and friendly".
He also said he believed America's European allies understood the need to "step up" to build a strong relationship.
"I think all of the European foreign ministers who come here this week will be bringing a very strong message. We have heard what you and the Obama administration have said about the commitment to work with allies.
"But we also know that allies have to step up to build a strong working relationship and I think all the European foreign ministers who come here don't just come with great expectations," Mr Miliband said.
Mrs Clinton also said that she discussed with Mr Miliband the row over Iran's nuclear activities.
"It is clear that... Iran has an opportunity to step up and become a productive member of the international community," Mrs Clinton said.
She repeated Mr Obama's message that the US was "reaching out a hand, but the fist has to unclench".
She added that senior US diplomat Bill Burns would be joining officials from six major powers - US, Russia, China, UK, Germany, and France - in Germany on Wednesday to discuss the Iran issue.
Tehran is subject to UN sanctions as some Western powers think it is trying to build a nuclear bomb, which it denies.
However, Mr Obama has signalled a willingness to re-define relations with Iran, holding out the prospect of dialogue after decades of mutual suspicion.
Mrs Clinton also thanked Mr Miliband for British military support in Afghanistan.
British forces are actively engaged against the Taleban, especially in the southern province of Helmand.