G7 must stand up to Russian aggression in Ukraine: Obama

US President Barack Obama urged fellow leaders of the G7 to stand up to "Russian aggression in Ukraine" as he enjoyed a traditional Bavarian welcome ahead of their summit in Germany.

 One of the many issues G7 leaders would be discussing during their two-day summit was "standing up to Russian aggression," Obama said in opening remarks as he was welcomed by German Chancellor Angela Merkel.

In a sign of togetherness designed to show absentee President Vladimir Putin the unity of the G7 over the Ukraine crisis, Obama said ties between the United States and Germany were "one of the strongest alliances the world has ever known."

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. 

For her part, Merkel praised the United States as an "essential partner" despite occasional "differences of opinion."

Traditionally strong US-German ties have been tested 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 Merkel under domestic pressure.

The US and Germany shared "common values", Merkel stressed, in an apparent reference to Putin whose Russia was expelled from the G7 after Moscow's annexation of Crimea. EU President Donald Tusk, also attending the meeting, said he wanted to "reconfirm G7 unity on sanctions policy" against Russia.

Obama and Merkel were speaking in the tiny village of Kruen ahead of the two-day summit at the nearby Elmau Castle. As well as Ukraine, the leaders are also expected to discuss the Greek debt crisis and the threat posed worldwide by jihadist terrorism.