Theresa May is set to challenge Donald Trump on climate change when she meets him at the G20 summit in Hamburg.
The prime minister will hold one-to-one talks with the US president at the two-day event, which will be dominated by North Korea's missile test.
She will tell Mr Trump an international agreement on tackling climate change should not be renegotiated.
It comes after Mr Trump controversially withdrew America from the Paris Agreement - a deal to combat global warming set to come into force in 2020.
A senior Government official said Mrs May would stress Britain "remains fully committed" to the agreement.
It is her first major meeting with the US president since her visit to the White House in January.
Back then, she was the first world leader through the doors of the White House after Mr Trump became president, and he predicted the pair would have a "fantastic" relationship.
But discussions they had were overshadowed when photographers briefly captured them holding hands as they walked from the Oval Office to their first press conference together.
Mrs May invited the president on a state visit to the UK but speculation that it may have been put on hold in the face of expected protests was fuelled by its absence from last month's Queen's Speech.
Protests are also expected as Mr Trump visits Warsaw in Poland before heading to Hamburg for the summit.
He will also attend the Bastille Day celebrations in France on July 14.
The G20 summit comes amid unease in Europe about the Trump administration's "America First" approach to trade and other issues.
German Chancellor Angela Merkel stood by her suggestion Europe can no longer reply entirely on the US and declared Germany could work with China to help calm the world's problems.
Mrs Merkel is hosting the G20 summit on Friday and Saturday in Hamburg.
The gathering should make for a challenging combination of world leaders, with Russian leader Vladimir Putin and Turkish President Recep Tayyip Erdogan also attending.
Police have already clashed with hundreds of protesters who are camped less than a mile from where the G20 leaders will be meeting.
Pepper spray and water canons were used to bring the crowd under control on Tuesday night.
The 'Welcome to Hell' demonstration is one of dozens of protests registered under a variety of themes - including a far-right pro-Trump rally - with more than 100,000 demonstrators from across Europe and beyond due to take part.
Officials expect 8,000 from Europe's violent left-wing scene, and have been tracking known activists coming in from Scandinavia, Switzerland, Italy and elsewhere.
On Wednesday, hundreds of people painted like clay figures moved slowly and silently through the streets of Hamburg to protest against the summit.