Top G7 energy officials have failed to agree on language for a joint declaration because of the US administration's review of policies related to climate change and the reduction of greenhouse gases.
Italy's economic development minister Carlo Calenda told a news conference that those areas remained "key priorities for other G7 countries and the EU" but that the United States "reserves its position" while the review is under way.
"Therefore it was not possible to sign a final joint declaration, since it would not cover the whole range of topics in the agenda," he said.
Energy Secretary Rick Perry led the US delegation to the talks that were being closely watched by climate change activists after President Donald Trump signed an executive order that was part of his pledge to undo much of his predecessor's efforts against global warming.
While campaigning for president, Mr Trump pledged to "cancel" the Paris Agreement, the first international deal to curb greenhouse gas emissions from both rich and poor countries.
President Barack Obama enthusiastically supported the agreement, which was adopted by the US and more than 190 other countries in 2015.
Another official at the talks said the meeting failed to agree on a draft joint statement because it included a reaffirmation of commitments made under the Paris Agreement.
"Perry and his team were not ready to accept that, mainly on the argument that they are reviewing their policies and have not yet taken a position on the Paris Agreement," he said.
There was no immediate response to a request for comment from the US delegation.
Mr Trump's order launched a review of the Clean Power Plan, Mr Obama's effort to restrict greenhouse gas emissions from coal-fired power plants.
Mr Trump also lifted a 14-month halt on new coal leases on federal lands.
EU Climate and Energy Commissioner Miguel Arias Canete noted that except for the United States, all G7 nations joined the EU in reaffirming their determination to implement the Paris Agreement.
"We see climate action and the clean energy transition for what it is: a driver of jobs and economy growth, a moral imperative and a promise for a better future," he said.
Officials noted that said consensus was reached on co-operation to support energy security in Ukraine, the future role of natural gas and cybersecurity in the energy sector.
Greenpeace activists protested outside, calling on officials to maintain their commitments to reduce greenhouse gases under the 2015 Paris Agreement.