Obama applauds German Chancellor Merkel's pro-refugee stance

US President Barack Obama on Sunday leapt to the defence of Chancellor Angela Merkel, saying the German leader, facing fire at home over a record refugee influx, is on the "right side of history".

"What's happening with respect to her position on refugees here, in Europe, she's on the right side of history on this," said Obama on his fifth and final official visit to Germany.

Lauding Merkel for taking "very tough politics not just to express a humanitarian concern but also a practical concern", the US leader said, "She is giving a voice to the kinds of principles that bring people together rather than divide them."

Merkel has faced virulent criticism in Germany over her liberal stance after 1.1 million asylum seekers arrived in Europe's top economy last year.

Critics, particularly from within her conservative camp, argue that Germany is ill-equipped to cope with the sheer scale of the arrivals.

Merkel recently helped Europe and Turkey negotiate a deal to help ease the migrant flow.

She is giving a voice to the kinds of principles that bring people together rather than divide them

But Turkey stood its ground over the contentious issue of visa-free travel for its citizens on Saturday, warning Merkel and top EU officials it would stop taking back migrants from Europe if the bloc failed to keep its word.

"The issue of the visa waiver is vital for Turkey," Prime Minister Ahmet Davutoglu said at a joint news conference with Merkel, European Council head Donald Tusk and European Commission Vice President Frans Timmermans.

Merkel also insisted that her proposal for safe zones in Syria is consistent with international efforts to bring peace to Syria.

Germany's allies, particularly the United States, have dismissed the idea of a ground-based military intervention in Syria to protect civilians.

Merkel met with President Barack Obama on Sunday, and said afterward that the proposal wouldn't require outside intervention.

Merkel says creating safe zones should be part of peace negotiations that involve the Syrian government and moderate opposition groups.

Obama says the idea of making safe zones controlled by moderate opposition part of the peace talks shows that "here there's no space between us."