US President Donald Trump and German Chancellor Angela Merkel plan to meet Thursday for what are expected to be tricky talks on the eve of a Group of 20 summit.
Merkel's spokesman Steffen Seibert said that "a meeting with the US president is planned before the G20 summit, most probably in the early evening of Thursday".
Transatlantic differences on climate change, trade, defence spending, refugees and other issues are expected to cloud the July 7-8 meeting of world leaders from major industrialised and emerging economies in the northern port city.
Last week Merkel met with key European leaders and vowed to make a stand for climate protection and open markets at the meeting with Trump, who has said he will take the US out of the Paris climate deal and pursue a protectionist "America First" policy.
Merkel said last Thursday that "the differences are obvious and it would be dishonest to try to cover that up. That I won't do."
She also said the US exit from the 2015 Paris climate pact had made Europe "more determined than ever" to make the accord a success.
On Monday, presenting her party's election platform, she predicted that at the G20 "we are going to have a whole series of thorny issues".
"We know the positions of the US government and I do not expect them to disappear on a two-day trip to Hamburg," the chancellor said.
She warned against high expectations for the summit, noting that the final communique has to be "approved unanimously".
She said that while there would be common ground on combating terrorism financing, "in other areas there are many differences".
More than 20,000 police will be on duty in Hamburg for the meeting, whose participants include China's President Xi Jinping, Russia's Vladimir Putin and Turkey's Recep Tayyip Erdogan.
More than 30 anti-capitalist protests have been scheduled for before and during the meeting.
A day before the G20 starts, Trump will head to Warsaw for a meeting of central and eastern European leaders likely to include Hungary's hardline Prime Minister Viktor Orban, who has sparred with western European leaders, especially on the refugee issue.
