British Prime Minister Theresa May has told US Republicans the UK and America must stand up for their interests but cannot return to "failed" interventionist policies.
At the start of her visit to the US, she called on US President Donald Trump to build a stronger "special relationship" between Britain and the United States to withstand new, modern-day threats.
Her visit to the US follows controversial comments by Mr Trump about waterboarding.
The prime minister has said the UK condemns torture and that would not change.
Before her talks with Mr Trump, Mrs May travelled to Philadelphia to address Republican leaders at an event attended by the US president.
In her speech, Mrs May said: "It is in our interests - those of Britain and America together - to stand strong together to defend our values, our interests and the very ideas in which we believe."
That could not mean a return to failed policies, she said. "The days Britain and America intervening in sovereign countries in an attempt to remake the world in our own image are over. But nor can we afford to stand idly by when the threat is real and when it is in our own interests to intervene."
On the plane to the US, Mrs May said both countries shared many values and that contrary to his statements that Nato was "obsolete," Mr Trump had told her he was committed to the US-led military alliance.
Pressed on whether Britain's often cautious prime minister would get on with the "brash" US president, Mrs May said: "Haven't you ever noticed ... sometimes opposites attract?"
"What's going to be important is having the opportunity to actually sit down with President Trump and talk to him face to face, about the interests we share, about the special relationship, about the joint challenges we both face."
She planned to raise security and defence, Syria, Russia and NATO with Mr Trump, refusing to rule out discussions where the two leaders may not see eye-to-eye.
Asked about the possibility that Mr Trump could bring back a CIA program for holding terrorism suspects in secret overseas prisons where interrogation techniques often condemned as torture were used, she said said: "We condemn torture and my view on that won't change - whether I'm talking to you or talking to the president."
Under current rules, the UK military cannot use information obtained by torture or join operations where it might take place.
Some kind of trade agreement is high on her list of priorities, despite Britain and the United States being at odds over genetically modified organisms, meat production and public procurement and Mrs May unable to sign deals until after Brexit.
Mrs May said she would launch the divorce talks by the end of March by triggering Article 50 of the EU's Lisbon Treaty, which gives up to two years to negotiate an exit deal. Only then can she agree with third countries.
"I think there is much that we can do in the interim in terms of looking at how we can remove some of the barriers to trade in a number of areas so that we are able to see an advantage for both of us even if we haven't actually been able to sign that legal free trade agreement," she said.
"We're both very clear that we want a trade deal."
- Reuters / BBC