"The president said that he looks forward to helping Chancellor Merkel make the Summit a success", the White House said of Monday's call.
The informal meeting will be attended by the BRICS leaders, who will hold their summit in September in Xiamen, south China.
The day before the US celebrates its Independence Day, President Donald Trump is conducting foreign policy with other world leaders by phone. Trump also thanked Gentiloni for Italy's efforts in addressing the Libyan migration crisis.
German Chancellor Angela Merkel says she expects the Group of 20 leading economies to broadly agree on tackling global terrorism at a summit in Hamburg later this week.
"I think there's a strong sense among EU leaders that they need to take responsibility for their positioning in the world", said Susi Dennison, a senior fellow at the European Council on Foreign Relations.
The White House said Trump and Xi "reaffirmed their commitment to a denuclearized Korean Peninsula", while Trump also raised the threat of North Korea's ballistic missile program.
Djokovic beats Medvedev to reach Eastbourne final
Andy Murray begins his quest for a third Wimbledon title over the next fortnight after his triumphs in 2013 and a year ago . At a set down and 3-3 in the second she forced seven dueces in an attempt to break the Czech's serve .
Yankees' Dustin Fowler Suffers Knee Injury in MLB Debut, Will Undergo Surgery
Fowler made his Major League debut June 29. "Maybe you put up Plexiglass, so they can't flip over and people can look through it". Left fielder Brett Gardner told reporters following the game that it was the worst thing he had seen while on a baseball field.
Treasury announces new sanctions to increase pressure on North Korea
Treasury Secretary Steven Mnuchin announced that the US has sanctioned two Chinese citizens, a shipping company, and a bank. It cited a United Nations expert panel as saying the company has violated a ban on trade in luxury goods with the North.
Putin and Trump are to hold their first meeting there.
Earlier in the weekend, Mr. Trump had called Chinese President Xi Jinping, and "reiterated his determination to seek more balanced trade relations with America's trading partners", the White House said.
The protest Sunday was one of 30 planned in the German city in anticipation of the two-day summit, which begins Friday.
People protest against the gathering of European leaders on the upcoming G-20 summit in Hamburg, Germany, Sunday, July 2, 2017.
The July 7-8 G20 Hamburg summit is expected to focus on issues of global economic growth, trade, spread of digital technology, climate policy and Africa's development, among others.