WASHINGTON (Reuters) - U.S. President Donald Trump discussed hot-button issues like climate change, trade and migration in calls with German and Italian leaders on Monday, before a summit this week of the G20 leading economies that could expose sharp policy differences.

Trump is preparing for the two-day Group of 20 meeting that starts in Hamburg, Germany, on Friday, just over a month after a G7 summit in Sicily showed deep divisions between Trump and other Western leaders on such issues.

A fractious first NATO summit with Trump also left European allies wondering where the military alliance goes next.

Trump will hold separate meetings with various leaders in Hamburg, including host German Chancellor Angela Merkel, and a potentially difficult first meeting with Russian President Vladimir Putin.

A White House official said on Monday night that Trump held an “extensive discussion” by telephone with Merkel, focusing on issues including trade and climate change.

A little over one month ago, Trump said the United States was withdrawing from an international agreement aimed at reducing global carbon emissions that are blamed for climate change.

The Trump administration is also pressuring G20 nations to take steps to reduce global steel oversupply and other distortions in that market.

FILE PHOTO: U.S. President Donald Trump arrives at the Celebrate Freedom Rally in Washington, U.S. July 1, 2017. REUTERS/Yuri Gripas/File Photo

The White House said that in a separate conversation with Italian Prime Minister Paolo Gentiloni, Trump “underscored his appreciation for Italy’s efforts to address the significant Libyan migration crisis.”

In remarks last week, Merkel raised the prospect of an open clash with Trump at the Hamburg summit, although some Trump administration officials have played down the discord.

Heather Conley, a State Department official during Republican President George W. Bush’s administration, said the United States’ European allies were still shocked after the G7 and NATO summits with Trump cast doubt over Washington’s relation with its allies.

“There’s concern he could improve it – but could also do further damage,” said Conley, who is now with the CSIS think tank in Washington.

TRUMP-PUTIN MEETING

Russia and the United States are still discussing the timing of the encounter between Trump and Putin, a Kremlin aide said on Monday.

Since Trump was elected last November, Russia has been keenly anticipating the Republican president’s first meeting with Putin, hoping it would trigger a reset in U.S.-Russia relations that plunged to post-Cold War lows under Trump’s Democratic predecessor, Barack Obama.

But with Trump embroiled in controversy at home over his associates’ potential links to Moscow, the session with Putin has become a minefield. Too warm a meeting would allow Trump’s domestic opponents to accuse him of being a Kremlin stooge.

U.S. diplomat Thomas Shannon met on Monday with Russia’s ambassador to Washington, Sergei Kislyak, to prepare for the Trump-Putin meeting, the State Department said.

They also discussed scheduling a new meeting between Shannon and Russian Deputy Foreign Minister Sergei Ryabkov, which Moscow canceled in June in anger at expanded U.S. sanctions on Russia.