US President Barack Obama (L) and Germany's Chancellor Angela Merkel (R) enjoy a beer at a breakfast meeting with local citizens in Kruen near Garmisch-Partenkirchen, southern Germany, on June 7, 2015.(AFP)

© 2015, The New York Times News Service

President Barack Obama sought to smooth over tensions with a crucial ally, bonding Sunday with Chancellor Angela Merkel of Germany over beer, sausages and their shared determination to confront Russia over its aggression in Ukraine, as he declared her a "great friend and partner" during a summit meeting of world leaders.Greeting Merkel with an embrace and kisses on both cheeks near a picturesque town square at the foot of the Alps, Obama emphasized the ties that bind Germans and Americans despite a troubled history."The fact that all of us are here together today is proof that conflicts can end, and great progress is possible," Obama told about 800 townspeople, many of them wearing traditional dress. "We stand together as inseparable allies, in Europe and around the world."The meeting came at the start of the Group of 7 conference Merkel is hosting at a castle and luxury resort, where the leaders of the major industrialized nations are meeting to discuss the global economy, climate change, terrorism, and, as Obama said, "standing up to Russian aggression in Ukraine."He and Merkel agreed that economic sanctions on Russia for its actions in Ukraine should not be lifted until a cease-fire there had been fully implemented and Moscow respected Ukraine's sovereignty. The White House intensified its criticism of President Vladimir Putin of Russia as Obama pressed for a firm commitment from Europe during the two-day gathering to preserve the sanctions, along with a broader statement of resolve to punish Russia for further escalations in Ukraine.Russian-backed separatists have been clashing violently with Ukrainian forces and massing heavy weaponry near the border, prompting the White House to say the cease-fire has been violated. The escalation apparently extended offshore Sunday into the Azov Sea, where a Ukrainian coast guard speedboat exploded after striking a mine near the port of Mariupol.With the European Union facing a vote this month on whether to continue the sanctions, Obama has made stiffening resolve on the issue a prime objective."We think that there can be a peaceful, diplomatic resolution to this problem, but it's going to require that Europe, the United States and the trans-Atlantic partnership, as well as the world, stay vigilant and stay focused on the importance of upholding the principles of territorial integrity and sovereignty," Obama said during a meeting with the British prime minister, David Cameron.The meetings unfolded after a period of strain between Obama and Merkel. Although Obama enjoys an unusually close rapport and strong working relationship with Merkel, their bond has been tested by a complicated intelligence relationship that has proved to be a political vulnerability for the chancellor.Those strains did not prevent her from inviting Obama to tour a historic village here before the summit meeting opened, in a carefully choreographed event showcasing their friendship."Although it is true we sometimes have differences of opinion today from time to time," Merkel said, "the United States of America is our friend, our partner and indeed an essential partner."Merkel is facing harsh criticism here that she is doing the bidding of the National Security Agency, after allegations surfaced in April that Germany's foreign intelligence service was monitoring European companies and perhaps individuals at the U.S. intelligence agency's behest.The uproar is not the first time spying has become a bone of contention between Obama and Merkel. In 2013, documents released by Edward J. Snowden suggested the NSA had tapped Merkel's personal cellphone for a decade. That practice, once revealed, was halted by the president. And last summer, tensions grew when Merkel's government expelled the CIA station chief in Germany after Berlin said it found evidence of U.S. spies recruiting at least one German official.The NSA surveillance issues have "obviously cast a very dark shadow on their personal relationship," said Julianne Smith, a former deputy national security adviser to Vice President Joe Biden and now director of the Strategy and Statecraft Program at the Center for a New American Security in Washington.But there is little doubt that Obama, who tends to prioritize strategy and shared interests over personality in his relationships with world leaders, needs Merkel, and that she needs him. Merkel has been important in rallying Europe to stay united against Russia's interference in Ukraine, even as the economic sanctions designed to pressure Putin place political strain on her and many of her counterparts."The commitment required by our European partners to implement and maintain these sanctions is significant," said Josh Earnest, the White House press secretary. "They have economies that are more integrated with Russia than the United States has, and so we recognize that many of the countries that we're counting on to continue to enforce these sanctions are countries who do so at some sacrifice to their own economy."The White House said Obama and Merkel also discussed their shared support for a major trans-Atlantic trade deal; the prospect of teaming up to reach an agreement on climate change by reducing global greenhouse gas emissions and countering the Sunni militant group the Islamic State."These are the priorities in our relationship," Earnest said.During Obama's nearly 45-minute meeting with Merkel on Sunday, neither raised the issue of NSA surveillance, Earnest said, while more than half of the session was taken up with talk of Russia and Ukraine."They realize that they continue to share a common agenda on Russia, on a number of fronts," Smith said. The president "continues to reach out to her," she said, adding, "I think they still trust each other."At the same time, a year after the seven world powers banded together to kick Russia out of their group, the White House seemed determined to use the gathering to portray Putin as an international pariah."Russia has essentially thumbed their nose at the commitments that they made" in a cease-fire agreement with Ukraine, Earnest said, indicating that Moscow is supplying, leading, training and otherwise backing separatists in Ukraine. "Russia's failure to live up to those commitments is what leads to their increasing isolation and the increasing costs being imposed on their economy."Any disputes seemed remote Sunday as Obama and Merkel sampled local food and strolled through town greeting men wearing lederhosen and women in dirndls. The president halfheartedly asked Merkel if the summit meetings, which are being held at a lush spa resort nearby, could instead take place in the small alpine town's center, over beer."It was a very fine beer," Obama said on his way out of the village. "I wish I was staying."