Leaders from the G7 industrial nations have backed a tough line towards Moscow at the start of a summit in the Bavarian Alps, with US President Barack Obama urging the gathering to stand up to Russian aggression in Ukraine.

The crises in Ukraine and Greece seemed likely to overshadow the economic discussions at Schloss Elmau, a luxury Alpine hotel near the Austrian border.

Obama said leaders would discuss the global economy, trade partnerships and "standing up to Russian aggression in Ukraine," as well as threats from armed groups and climate change.

British Prime Minister David Cameron and European Council President Donald Tusk both said they hoped the G7 would present a united front on sanctions towards Russia.

EU leaders agreed in March that sanctions imposed over Russia's intervention in Ukraine would stay until the Minsk ceasefire agreement was fully implemented, effectively extending them to the end of the year, but a formal decision has yet to be taken.

Italian Prime Minister Matteo Renzi is known to be sceptical about sanctions and left-wing politicians in Germany have also called for them to be removed.

"If anyone wants to start a discussion about changing the sanctions regime, it could only be about strengthening it," said Tusk in reaction to the requests in question.

European monitors have blamed a recent upsurge in violence in eastern Ukraine on Russian-backed separatists. Russian President Vladimir Putin was frozen out of what used to be the G8 after Moscow's annexation of Crimea last year.

Other agenda items

During the talks, host Angela Merkel, the German chancellor, was hoping to secure commitments from her G7 guests to tackle global warming ahead of a major UN climate summit in Paris in December. The German agenda also foresees discussions on global health issues, from Ebola to antibiotics and tropical diseases.

European Commission President Jean-Claude Juncker, speaking before the start of the summit, voiced exasperation with Greek Prime Minister Alexis Tsipras, who has dismissed the latest aid-for-reform proposal from international creditors as "absurd".

Athens is running out of cash and will default on its debt, a move that could end up pushing it out of the eurozone, if it fails to reach a deal with its European partners and the International Monetary Fund in the coming weeks.

Juncker reaffirmed that a so-called "Grexit" was not an option being considered, but said this did not mean he could "pull a rabbit out of a hat" to prevent it.

Leaders and reporters were shuttled to the summit site by helicopter on Sunday morning as hundreds of protesters blocked the main road to Schloss Elmau.

Source: Reuters