Still, Trump's gambit may further inflame tensions with other leaders, including British Prime Minister Theresa May.
Trump also fumed about Canadian Prime Minister Justin Trudeau as their differences on trade and tariffs have been publicly revealed.
A senior British government source said Russian Federation needs to change its approach before any conversation about it rejoining the G7 can begin.
Trudeau, UK Prime Minister Theresa May, German Chancellor Angela Merkel and French President Emmanuel Macron all oppose Trump's trade policies, and along with Mexico vowed to impose retaliatory tariffs on United States goods.
Russia was ousted from the group after the annexation of Crimea by pro-Russian separatists in 2014.
The annual G7 summit brings together the leaders of the USA, UK, Germany, France, Japan, Italy, Canada and the European Union - but this year it's being dominated by one man: Donald Trump.
Conte's decision to side with the U.S. may irritate his European allies, who have so far declined to make any overtures to Russian Federation - though previous Italian governments have expressed hopes that Russian Federation would one day return, as has Japan.
Tusk warned that "the rules-based worldwide order is being challenged, quite surprisingly not by the usual suspects but by its main architect and guarantor, the U.S.".More news: Whittaker Makes the Mark; Romero Does Not
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"We will not stop trying to convince our American friends and President Trump that undermining this order makes no sense at all because it would only play into the hands of those who seek a new post-West order where liberal democracy and fundamental freedoms would cease to exist", said Tusk.
The commander in chief plans to skip the climate change and environment portion of the G7 and leave early for Singapore for his historic meeting with North Korean dictator Kim Jong Un.
Russian President Vladimir Putin is meeting with his Chinese counterpart Xi Jinping in Beijing at the start of a state visit ahead of a summit featuring their two countries and six Asian states.
"Looking forward to straightening out unfair Trade Deals with the G7 countries", Trump tweeted. The two have met more than 20 times.
It is disappointing that the United States unilaterally withdrew from the Iran nuclear deal, said the statement, adding that China and Russian Federation will try their best to safeguard the deal and take note of the extreme importance of protecting the interests of all parties who engage in economic and trade cooperation with Iran from unilateral imposition of long-arm jurisdiction.
Trump railed against trade deficits with other countries.. He declared, "We have to straighten it out". "All this tells me that dialogue can be constructive".
"It won't even be hard and in the end, we'll all get along".
A few days ago, the Trump dispensation slapped stiff tariffs on steel and aluminum imports on five of its six G7 partners. You know, whether you like it or not, and it may not be politically correct, but we have a world to run.
Yesterday, Macron tweeted, "The American president may not mind being isolated, but neither do we mind signing a six-country agreement, if need be".