WASHINGTON (AP) -- President Barack Obama plans to urge European leaders this weekend not to waver from sanctions against Russia, pursuing what the White House is calling a "steady as she goes" policy while accusing Moscow of flagrantly violating a ceasefire agreement in Ukraine.

For the second year in a row, Russia's moves on Ukraine are looming over the Group of Seven summit, which is bringing leaders of the world's largest industrialized democracies to Germany for two days of meetings starting Sunday. The gathering comes a year after the leaders booted Russian President Vladimir Putin from their group in protest over the Ukraine crisis that now has killed more than 6,400 people.

Canadian Prime Minister Stephen Harper told The Associated Press that Russia should never be allowed back in the G-7 as long as Putin is president.

White House officials said they are concerned by a sudden outburst of violence in eastern Ukraine this week, despite economic penalties against Moscow and a four-month-old cease-fire agreement signed in Belarus.

"Clearly, President Putin's calculus has not fully shifted. We continue to see very concerning Russian aggression in eastern Ukraine," Obama deputy national security adviser Ben Rhodes said in a conference call with reporters to preview the trip. But he argued that continuing sanctions is the right course because they are a deterrent against more aggressive Russian action and need more time to work - noting it took years of sanctions to bring Iran to negotiations over its nuclear weapons program.

"That is why it's so important that sanctions are kept in place, so that they're not just seen as one-time punishments that are then able to be waited out by countries that continue to violate international law and international norms," Rhodes said. "But rather, we need to maintain the pressure, show that there cannot be cracks in the transatlantic unity, and show that the costs are just going to continue to grow for Russia."

European leaders must decide later this summer whether to extend their sanctions, and the White House officials said Obama's focus will be on encouraging them to take that step. But unless there's a significant escalation of the crisis, the U.S. and European Union appear to have little appetite for tougher penalties against Russia.

"I don't see any change in policy on Ukraine, nor do I see Ukraine fatigue. I think our general view is steady as she goes on that front," said Charles Kupchan, senior director for European affairs at the National Security Council. "We hold open the possibility that sooner or later the Russians will comply with the Minsk agreements, and that we can end this diplomatically."

At the G-7 meeting at the Schloss Elmau, a one-time Bavarian artist retreat turned luxury spa, Obama will join the leaders of Britain, Germany, France, Italy, Canada and Japan. The prime ministers of Canada and Japan planned to visit Ukraine on their way to Germany.

Obama plans to open his trip by meeting German Chancellor Angela Merkel and delivering a speech in the picturesque Alpine village of Krun. He also plans to meet privately with British Prime Minister David Cameron for the first time since Cameron's re-election last month, and with Iraqi Prime Minister Haider al-Abadi, who is attending to discuss the Islamic State terror threat in his country.

As they prepare to gather, Defense Secretary Ash Carter has summoned American defense and diplomatic officials for meetings Friday in Germany on countering Russia and assessing the effectiveness of the sanctions and U.S.-backed military operations.

Carter wants advice on whether the U.S. needs to expand military exercises or step up assistance to other countries in the region who are worried about the threat to them. A senior U.S. official traveling with Carter provided details about the meetings on condition of anonymity but was not authorized to publicly discuss details of the gathering.

Carter and others suggest the U.S. should consider providing lethal weapons to Ukraine.

The armistice required both sides to pull back heavy weapons from the front line, but international observers regularly note violations across the board. Regular reports of casualties among government and separatist fighters have continued. But deaths among noncombatants had almost ceased until recent days, in an indication that the warring sides are again increasingly resorting to indiscriminate shelling.

"We see all along the line of contact use of artillery and other military actions that are inconsistent with both the fact and the spirit of the agreement," Kupchan said. "And how the United States and its allies can put pressure on the Russians to adhere to the commitments will be on the table at Schloss Elmau."

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Rob Gillies contributed to this report from Toronto.