The leaders of Germany and the United States hammered home a tough line on Russia Sunday as they kicked off a G7 summit dominated by crises in Ukraine and Greece.

German Chancellor Angela Merkel began proceedings by treating US President Barack Obama to some traditional Bavarian beer garden hospitality, with frothy ale, pretzels and oompah brass music played by locals in lederhosen.

But after the smiles in the sunshine, the two issued a stark warning to President Vladimir Putin over what Obama said was his “aggression” in Ukraine.

“The two leaders… agreed that the duration of sanctions should be clearly linked to Russia’s full implementation of the Minsk agreements and respect for Ukraine’s sovereignty,” a statement from the White House said, referring to a ceasefire deal struck in the Belarus capital.

The folksy welcome and display of US-German unity contrasted sharply with the leaders’ line on Russia, which was excluded from the talks.

Merkel said later that Moscow should stay out of the G7 “community of values” for now over its actions in Ukraine.

“There is a barrier at the moment and I can’t really see how it can be overcome,” she told German public broadcaster ARD.

The Japanese and Canadian leaders had Saturday made a point of visiting Kiev on their way to Germany to voice support for Ukraine’s embattled leaders, as government troops again traded fire with pro-Russian rebels in the east.

A key G7 issue would be “standing up to Russian aggression in Ukraine,” Obama said ahead of the talks with Britain’s David Cameron, France’s Francois Hollande, Italy’s Matteo Renzi, Canada’s Stephen Harper and Japan’s Shinzo Abe.

A recent flare-up in fighting in east Ukraine has left at least 28 dead and sparked fears that the escalation will derail the hard-won ceasefire brokered by France and Germany four months ago.

The situation remained “tense” in eastern Ukraine, the Ukrainian army said, with eight soldiers wounded in the past 24 hours.