Pope Francis has asked Germany to keep fighting for the Paris climate change deal and to "tear down walls" that inhibit international cooperation, Chancellor Angela Merkel said on Saturday, offering a stark contrast between her agenda and US policy.

US President Donald Trump announced earlier this month that he would withdraw from the landmark 2015 global agreement to fight climate change, drawing anger from world leaders.

The two talked about ?the good relations and fruitful collaboration between the Holy See and Germany?, Vatican Radio ? the broadcasting station of the Pope's Ministry ? reported.

"The Pope encouraged me to continue and fight for international agreements, including the Paris agreement," Merkel told reporters after an unusually long, 40-minute private audience with him.

Merkel, who faces elections in September, said the Pope expressed his support for the agenda of the G20 major economies, which will hold a summit in Hamburg next month.

"This (G20) agenda assumes that we are a part of a world in which we work together through multilateral cooperation," Merkel said of her discussion with the Pope.

"It is a world in which we want to tear down walls and not build them, and in which we all seek prosperity, wealth, honour, and dignity for mankind."

Trump, who has promised to build a wall along the Mexican border, has shunned some multilateral cooperation.

The Vatican said that issues of common interest were discussed, including the need for the international community to focus on combating poverty, hunger, the global threat of terrorism, and climate change.