Leaders of the Group of Seven (G7) leading industrialized countries met on the Italian island of Sicily for what European Council President Donald Tusk said would "no doubt" be "the most challenging G7 summit in years."
Some of the participants hold "very different positions on topics such as climate change and trade," Tusk said before the two-day summit opened on May 26 in the resort town of Taormina.
"Most importantly, unity needs to be maintained when it comes to defending the rules-based international order," he said, warning that "if our group is not determined and united enough, the situation in the world can really get out of hand."
The G7 summit in Taormina is the first such meeting for U.S. President Donald Trump, who took office in January. Trump is expected to face questions from other leaders about his positions on trade and climate change.
The leaders are also due to discuss security cooperation following the May 22 bombing at a concert in Manchester, England, that killed 22 people and was allegedly carried out by a 22-year-old Briton of Libyan descent.
Tusk said that he "totally agreed" with Trump "when he said the international community, the G7, the United States, Europe should be tough, even brutal, with terrorism" and the Islamic State (IS) extremist group.
The summit kicked off with a ceremony at an ancient Greek amphitheater overlooking the sea, where the leaders stood together for a family photo against the backdrop of the Mediterranean.
"Getting ready to engage G7 leaders on many issues including economic growth, terrorism, and security," Trump tweeted before the summit."
Western news agencies quoted diplomatic sources as saying that Trump and the leaders of Britain, Germany, France, Italy, Japan, and Canada had similar views on many issues, but that Washington remained isolated on commerce and the environment.
Ahead of the summit, European Commission President Jean-Claude Juncker rejected reports that Trump had aggressively condemned German trade policies during a meeting in Brussels on May 25.
German media reports said Trump had denounced Berlin's policies as "very bad" and had signaled that he wanted to limit sales of German cars in the United States.
"He did not say that the Germans were behaving badly," Juncker said in Sicily ahead of the G7.
Juncker called the media reports exaggerated, saying it was "not true" that Trump had been aggressive toward Germany in the talks.
An unnamed senior Italian diplomat said Trump and the heads of Britain, Germany, France, Italy, Japan, and Canada had similar views on many issues ahead of the two-day summit, but Washington remained isolated on commerce and the environment.
European Union states want a clear U.S. pledge "to fight all forms of protectionism," the diplomat said. But they were struggling to convince the U.S. president of the merits of free trade.
"We will have a very robust discussion on trade and we will be talking about what free and open means," White House economic adviser Gary Cohn told reporters late May 26.
He also predicted "fairly robust" talks on whether Trump should honor a U.S. commitment to cut greenhouse-gas emissions under the 2015 Paris Agreement.
He said the president, who has dismissed global warming as a "hoax," would make a final decision when he returned home, but stressed that he would put economic development first.
European diplomats expect their leaders to put pressure on Trump about the Paris emissions deal, which has comprehensive support across the continent.
After visits to Saudi Arabia, Israel, and the Palestinian Territories, Trump met Pope Francis in Rome on May 24 and held talks May 25 with the heads of the European Union and the NATO military alliance in Brussels.
In a tweet on May 26, Trump said his first trip abroad had been "very successful."
"Just arrived in Italy for the G7. Trip has been very successful. We made and saved the USA many billions of dollars and millions of jobs."
With reporting by Reuters,AP, and AFP