Britain will continue to press the US to cut damaging emissions even if President Donald Trump pulls out of the Paris Agreement on climate change, Boris Johnson has said.
Mr Trump has said he will announce on Thursday whether he intends to go ahead with his election campaign pledge to withdraw from the landmark 2015 deal to reduce CO2 emissions.
The move has prompted alarm around the world with China and the EU reported to be ready to issue a joint statement saying the agreement is "an imperative more important than ever".
Mr Johnson said Britain still believed that international action was necessary to bring down emissions and slow the pace of global warming, and would be urging the US to play its part.
"We will continue to lobby the Americans and the White House to show the leadership they have shown in the past on reducing CO2," he told Sky News.
The Foreign Secretary said the US had already taken important steps to cut emissions, with many of key decisions being taken by individual states rather than the federal government.
"The states of the United States, where so many of the important decisions on emissions are taken, have already made a huge amount of progress and that progress will continue," he said.
"Further progress needs to be made by other countries - notably India, China and others. They are huge emitters. We need to tackle this globally."
The White House has signalled Mr Trump is likely to pull out of the agreement, although aides made clear that no decision was final until the president made his announcement.
Environmental campaigners have warned that US withdrawal would be disastrous, putting America on "the wrong side of history", although many were quick to say the transition to a clean economy is now unstoppable.
There have also been calls for the UK, which in recent days confirmed its commitment to climate action with the other G7 nations apart from the US, not to do trade deals with America if it pulled out.
Rumours about the future of US involvement in the Paris deal were further stoked when Mr Trump tweeted on Wednesday: "I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN!"
Nick Dearden, director of Global Justice Now, said: "Amidst the series of ill-informed and autocratic policies that Trump has enacted since coming to power, his decision to pull out of the Paris accord stands out as the one that will have the most long-term and disastrous consequences for the world."
Friends of the Earth's chief executive Craig Bennett said the organisation would campaign against any trade deal with the US if it "turns its back on its global responsibility to tackle climate change" .
"This short-sighted and dangerous decision will be met by opposition around the world: from ordinary people, to scientists, and political leaders - making the US a global outcast," he said.