Theresa May has insisted the UK is committed to the Paris Agreement on climate change as she faced criticism over her response to US withdrawal from the deal.
A decision by President Donald Trump to pull the US out of the world's first comprehensive accord on tackling climate change and seek renegotiated terms that are "fair" to America has drawn widespread international condemnation.
A statement issued by the leaders of France, Germany and Italy said the deal cannot be renegotiated, and that they remain committed to the "irreversible" accord and regard it as "a cornerstone in the co-operation between our countries, for effectively and timely tackling climate change".
In a phone call with the US president shortly after his White House announcement, Mrs May expressed her "disappointment" at the move and stressed the UK remains committed to the landmark 2015 agreement to curb greenhouse gas emissions.
But she faced fierce criticism for failing to add her name to the joint statement by President Emmanuel Macron, Chancellor Angela Merkel and Prime Minister Paolo Gentiloni.
Labour leader Jeremy Corbyn labelled Mr Trump's move to withdraw from the Paris Agreement as "reckless and dangerous" and accused Mrs May of "subservience" and a failure of leadership in not signing up to the statement.
At an election campaign event in York, he said: "Given the chance to present a united front from our international partners she (Mrs May) has instead opted for silence and once again subservience to Donald Trump.
"It's a dereliction of both her duty to this country and our duty to our planet.
"This is not the type of leadership Britain needs either to negotiate Brexit or stand up to defend our planet in an era of climate change."
Mrs May said: "I've made the UK's position on the Paris Agreement very clear. We remain committed to the Paris Agreement. It's an important international agreement on climate change.
"I made the UK's position clear to president Trump last week at the G7 meeting, as did the other G7 leaders, and I made the position clear to president Trump last night."
She said Canada and Japan had not signed the letter either, but all three countries have the same view that they remain committed to the deal.
She denied it showed she is subservient to Mr Trump, and said she had made it clear in her telephone call on Thursday night that the UK continues to support the agreement and the Government wanted the US to remain in the deal.
The accord commits countries to holding global temperature rises to "well below" 2C above pre-industrial levels, which will require global emissions to be cut to net zero by the second half of the century.
Scientists have warned failure to curb dangerous climate change will lead to sea level rises, more intense storms and flooding, more extreme droughts, water shortages and heatwaves as well as massive loss of wildlife and reduction in crop yields, potentially sparking conflict and mass migration.
Despite the decision by the US, the second biggest polluter after China, to pull out of the deal, many analysts suggest the shift to a low-carbon economy is now unstoppable, with renewable prices tumbling and new clean technology being developed and deployed.
Mr Trump's decision prompted criticism from many US business leaders, including clean tech entrepreneur and Tesla chief executive Elon Musk and Robert Iger, chief executive of the Walt Disney Company, who said they had resigned from the president's advisory council over the issue.
Announcing his decision on Thursday, Mr Trump claimed the Paris deal allows countries such as China and India to carry on polluting at the expense of the US economy and jobs.
He said the US would stop implementing measures to meet its commitments under the agreement to cut emissions by 26-28% on 2005 levels by 2025, and end funding for poor countries to cope with climate change.
Under the terms of the agreement, the US can give notice that it will withdraw three years after the deal entered into force, and the process of leaving will take another year.
This means the US would not be out of the Paris Agreement until November 4 2020, the day after the next presidential election.