Group of Seven (G7) environment ministers and officials are meeting in Bologna on Sunday and Monday to discuss issues ranging from climate change to sustainable development and litter at sea.

But earlier this month US president Donald Trump said he would withdraw the United States from the Paris Climate Agreement, drawing condemnation from other world leaders.

"Positions over the Paris accord are far apart ... and will remain that way," Italian Environment Minister Gian Luca Galletti said on the sidelines of the meeting.

Italy holds the G7 presidency for 2017.

German Chancellor Angela Merkel, French president Emmanuel Macron and Italian prime minister Paolo Gentiloni have said the Paris agreement cannot be renegotiated, urging their allies to speed up efforts to combat global warming.

German environment minister Barbara Hendricks said all seven countries had agreed on the need to take action but disappointment had been expressed at the US decision to leave the Paris Accord.

"There will be a final comuniqué tomorrow that will differentiate opinions," she said, without providing details.

Trump has said the Paris accord would undermine the US economy, cost jobs, and put the country at a permanent disadvantage compared with its competitors.

Scott Pruitt, head of the US Environmental Protection Agency (EPA), attended the morning meeting in Bologna but flew back to the United States on Sunday evening to attend Trump's first full cabinet meeting scheduled for Monday.

In a statement the EPA said Pruitt had emphasised it was time to move forward and find ways to engage with other countries to protect and use US natural resources.

"I believe engaging in international discussion is of the utmost importance to the United States when it comes to environmental issues," he said in the statement.

According to Patricia Espinosa, executive secretary of the UN Framework Convention on Climate Change, Pruitt told delegates in the opening session that the United States wanted to continue making efforts in combating climate change.

"He also mentioned he wants to engage with the (UN's) Climate Change secretariat," she said.

Trump said when he announced he was pulling out of the Paris accord that his administration would begin negotiations either to re-enter the deal or set up a new agreement on "terms that are fair to the United States".

Italy's Galletti said the United States was looking to take the climate change debate forward on a voluntary basis while Paris was a multilateral accord requiring monitoring, deadlines and transparency.

"That's a substantial difference," he said.

The United States is the world's second biggest carbon emitter behind China.

United Nations executive director for the environment Erik Solheim, present at the morning sessions, said G7 countries, excluding the United States were absolutely committed to move ahead with climate action whatever happened in the White House.

"We cannot allow one nation to derail what 190 other nations are happy to do," he said.