U.S. President Barack Obama urged the global community to stand up to "Russian aggression in Ukraine" at the start of Group of Seven (G7) summit in Germany.

"We're going to discuss our shared future, the global economy that creates jobs and opportunity, maintaining a strong and prosperous European Union, forging new trade partnerships across the Atlantic, standing up to Russian aggression in Ukraine, combating threats from violent extremism to climate change," Obama said in opening remarks as he was welcomed by German Chancellor Angela Markel, according to Euronews.

Merkel, the host of the summit, backed Obama's remarks, saying that we should send a strong message to Russia. Merkel and Obama held a pre-summit bilateral meeting.

"Not sanctions as an end to itself, but sanctions to reach a target," Merkel said, according to Reuters.

"The duration of sanctions should be clearly linked to Russia's full implementation of the Minsk agreements and respect for Ukraine's sovereignty," the White House said in a statement after Obama and Merkel's meeting, reported The National Post.

However, Russia said on Monday that the statements from G7 leaders taking a tough line on Russia offered nothing new.

"We also drew attention to the fact that among the participants of this meeting there are nuances in their approaches. Some talk about the need for dialogue with Russia and the impossibility of solving serious problems without this dialogue, so we continue watching closely," a Kremlin spokesperson said, according to Reuters.

European Council President Donald Tusk also backed sanctions against Russia, saying that "our group is not only a group political or economic interest, but first of all this is a community of values."

"And that is why Russia is not among us here today," Tusk said at the start of summit, according to an EU statement.

The two-day G7 summit, attended by leaders of industrialised nations Britain, Canada, France, Germany, Italy, Japan and the United States, was held in a resort in the Bavarian Alps.