Theresa May has said she was "dismayed" by Donald Trump's withdrawal of the US from the Paris climate change agreement - but failed to bring it up with him during their bilateral meeting at the G20 summit.
She defended the decision not to challenge the US president during their 50-minute bilateral head-to-head in Hamburg, which saw issues including post-Brexit trade.
Officials said the prime minister instead discussed it with Mr Trump as they walked between engagements.
Challenged on why she had not used her bilateral meeting to challenge him, she said: "I did bring the issue of the climate change agreement up with President Trump.
"I've had a number of conversations with him over the time I have been here at the G20."
Mr Trump confirmed his intention to withdraw from the deal consented to by his predecessor Barack Obama in June, saying he would seek a better deal for US workers.
Mr Trump previously described climate change as a hoax by the Chinese to damage US manufacturing.
Mrs May said she had urged Mr Trump to rejoin the agreement backed by 19 of the world's 20 most powerful economies, along with every other global nation bar Syria and Nicaragua.
"When I brought it up with him, what I did was I encouraged him to bring the United States back into the Paris agreement," she said.
"I continue to hope that is exactly what the United States will do."
In the summit's official declaration, the leaders of the world's most powerful economies "take note" of the decision of the US to withdraw from the deal.
The text adds "the leaders of the other G20 members state that the Paris Agreement is irreversible".
German chancellor Angela Merkel said Mr Trump's decision was regrettable, while French president Emmanuel Macron said he would host a summit in December to discuss the next steps on the agenda.