The G7 nations have demanded action from internet providers and social media firms against extremist content online, vowing to step up their fight against terrorism after the Manchester attack.

"The G7 calls for communication service providers and social media companies to substantially increase their efforts to address terrorist content," Britain, the United States and their G7 partners said in a statement.

Meanwhile, US President Donald Trump is still refusing to back the 2015 Paris Agreement to fight climate change, blocking efforts by world leaders meeting in Sicily to get the new US leader to endorse the treaty, Italy's prime minister said today.

But there is agreement on other issues such as Syria, Libya and fighting terrorism, Paolo Gentiloni told reporters in Taormina, Italy, where the heads of the world's seven major industrialised economies (G7) are meeting.

"There is one open question, which is the US position on the Paris climate accords ... All others have confirmed their total agreement on the accord," Mr Gentiloni said.

"We are sure that after an internal reflection, the United States will also want to commit to it," he added.

At her first G7 meeting since becoming prime minister, Theresa May was keen to avoid Britain's soon-to-be-launched talks to leave the European Union and focused instead on the fight against terrorism, days after a suicide bomber killed 22 people at a pop concert in Manchester, the worst attack on Britain since 2005.

Mrs May, who on Thursday raised concerns over intelligence leaks in the United States, met Mr Trump between sessions at the G7.

A spokesperson for Mrs May said she and Mr Trump reaffirmed their commitment to a post-Brexit trade deal at the summit.

Trump's views on climate change 'evolving' - White House adviser

G7 leaders had a "controversial" debate on climate change, German Chancellor Angela Merkel told reporters, with US President Donald Trump urged by everyone at the table to back the Paris Accords.

Earlier, Italian Prime Minister Paolo Gentiloni said Mr Trump was still considering the matter, but added that he believed Washington would in the end honour its commitment to cutgreen house gas emissions under the 2015 Paris Agreement.

White House economic adviser Gary Cohn said Mr Trump's views on climate change are evolving after the discussions.

"I think his views are evolving. He came here to learn. He came here to get smart. His views are evolving which is exactly as they should be. His basis for a decision ultimately is going to be what's best for the United States," said Mr Cohn.

Mr Gentiloni had gone into the summit acknowledging deep divisions but hoping for some degree of convergence on a way forward.

Mr Trump campaigned on a pledge to ditch the United States commitment to applying the 2015 Paris deal, which seeks to curb global warming by cutting carbon emissions.

He has yet to act on the threat, having said he would listen to what US partners have to say before making a decision on how to proceed.

The stalemate on climate change was mirrored by divisions between the US and the other six G7 countries over trade and migration at the annual summit, described by officials as the toughest in years.

The meeting is due to conclude tomorrow with a final statement which Italian officials have indicated will be a fifth of the originally planned length - if it can be agreed at all.

Officials were due to work through the night in an attempt to reach a compromise on the text.