US president Barack Obama urged fellow leaders of the Group of Seven (G7) to stand up to “Russian aggression in Ukraine” as he enjoyed a traditional Bavarian welcome ahead of the summit in Germany.

In his opening remarks as he was welcomed by German chancellor Angela Merkel, Mr Obama said one of the issues G7 leaders would be discussing was “standing up to Russian aggression”.

In a sign of togetherness showing Russian president Vladimir Putin the unity of the G7 over the Ukraine crisis, Mr Obama said ties between the United States and Germany were “one of the strongest alliances the world has ever known”.

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He also hailed the “enduring friendship” between the American and German people in a speech warmly applauded by Bavarians in traditional dress, quaffing beer and munching pretzels.

Vladimir Putin is on the wrong side of the G7. Photo: AAP

Ms Merkel praised the United States as an “essential partner” despite occasional “differences of opinion”.

Mr Obama and Ms Merkel were speaking in the tiny village of Kruen ahead of the summit which starts on Sunday at the nearby Elmau Castle.

Locals were dressed in their finest traditional Tracht – lederhosen (leather trousers) for the men, dirndl smocks for the women, and girls in dresses with their hair in neat plaits.

Later the leaders tucked into plates of white sausage and soft pretzels, washed down with local wheat beer.

“There’s never a bad day for beer and Weisswurst,” Mr Obama quipped, after calling out the Bavarian greeting of Gruss Gott.

A farmer who sat at their table said the brew was non-alcoholic.

Police kept protesters away from the world leaders in the Bavarian Alps. Photo: Getty

Traditionally strong US-German ties have been tested in recent years by a spying scandal, including the alleged tapping of Merkel’s mobile phone, and more recently by reports of joint US-German surveillance of European political and economic targets, which has put Ms Merkel under domestic pressure.

She stressed the US and Germany shared “common values” in an apparent reference to Mr Putin.

Russia was expelled from the G7 after Moscow’s annexation of Crimea.

European Council president Donald Tusk will also attend the meeting and said he wanted to “reconfirm G7 unity on sanctions policy” against Russia.

As well as Ukraine, the leaders are also expected to discuss the Greek debt crisis and the threat posed worldwide by jihadist terrorism.