Kemi Badenoch has said the US is acting in its national interest and the UK also needs to, ahead of Sir Keir Starmer's meeting with Donald Trump.
Ms Badenoch also said it is "absolutely critical" that Sir Keir succeeds in his talks on ending the war in Ukraine with Mr Trump on Thursday.
On Monday, the US sided with Russia on two UN resolutions when they declined to condemn Russia's war in Ukraine, and backed a resolution for the conflict's end that avoided labelling Russia as the aggressor or acknowledging Ukraine's territorial integrity.
The Conservative leader, giving a foreign policy speech in London on Tuesday, told Sky News' political editor Beth Rigby the US is "not an authoritarian regime" and shares the same Western values as the UK, including free trade, free enterprise and free speech.
Ms Badenoch said the UK must "accept reality" that the world has changed and "we can no longer hide behind vapid statements that were at best ambitious 20 years ago and are now today outright irrelevant".
