DEAUVILLE, France — President Barack Obama and Russian President Dmitry Medvedev emerged from private talks Thursday unable to show progress on the contentious issue of missile defense, underscoring an enduring mistrust underlying the U.S.-Russia relationship despite gradual thawing.

Obama's top Russia adviser Mike McFaul put the problem plainly after the meeting with the Russians: "They don't believe us," he said.

At issue is Washington's plan to site missile interceptors in Central and Eastern Europe in phases through 2020. Despite repeated assurances, Russia hasn't let go of the fear that the U.S. would end up threatening Russia's own missile arsenal, something U.S. officials say won't happen.

Obama and Medvedev spoke on the sidelines of a two-day summit of industrialized nations here focused in part on bolstering emerging democracies in the Middle East and North Africa.

Obama said after the 90-minute meeting with Medvedev that they'd committed to working together on missile defense to find an approach that is "consistent with the security needs of both countries, that maintains the strategic balance, and deals with potential threats that we both share."

Medvedev, however, suggested the problem wouldn't be solved anytime soon.

"I have told my counterpart, Barack Obama, that this issue will be finally solved in the future, like, for example, in the year 2020, but we, at present, might lay the foundation for other politicians' activities," Medvedev said. "And this would be a sound foundation for cooperation between our two countries in the future."

Medvedev has warned that failure to cooperate with Moscow on the missile shield could spark a new arms race.

Their meeting came in the context of an ongoing attempt to shore up relations between the U.S. and Russia, once icy but now significantly warming — to the point that Obama and Medvedev had a memorable bonding day, complete with a burger run, when the Russian president visited the U.S. less than a year ago.

But deep tensions remain and the leaders' body language Thursday seemed to show it. Obama's stern expression was in contrast to his relaxed and affable demeanor during earlier stops on his four-country Europe tour. Medvedev also appeared cool, and leaned away from Obama as he talked. The two men spoke of a strengthened personal relationship, but their body language did not match their words.

Obama's aides worked later to correct any impression, based on the leaders' cool demeanor in their few minutes of speaking in front of the media, that there was tension between the men.

Deputy national security adviser Ben Rhodes described the relationship as warm and free-flowing, saying they even "joke around a lot."

McFaul said it was precisely because of their much cultivated relationship that Medvedev and Obama were talking seriously about issues that have stymied their countries for decades, such as missile defense.

"It was not stern," McFaul said of the session between the leaders, which he sat in on.

At the same time White House officials said that after decades of deep mistrust during the Cold War, and the chilly relationship between former presidents George W. Bush and Vladimir Putin, putting past feelings aside will take time.

"This is a very hard issue," McFaul said. "There's a lot of old thinking in both of our governments, frankly. This is a new challenge to think about how to do this cooperatively."

Medvedev, according to a translator, said he was "satisfied" by his personal relationship with Obama and that it has helped advanced the one between the countries, too.

"It requires a lot of effort, and it requires continuing in the same vein, full of trust, with relations full of trust, between the two presidents," the Russian president said. "It does not mean that we'll have common views and coinciding views on all the issues. It's impossible, and it's not worth trying."

After their one-on-one meeting, Obama and Medvedev walked the short distance to the G-8 summit site to meet the host, French President Nicholas Sarkozy. Along the way, Obama stopped to shake hands with onlookers behind metal barricades, many wearing blue plastic ponchos against the overcast skies at this seaside resort.

Obama planned to use the summit to work with leading economies on ways to support fledgling democratic transitions in Tunisia and Egypt, while also creating incentives to encourage other countries in the region to pursue greater political freedoms.

The summit comes on the heels of Obama's sweeping address at London's Westminster Hall Wednesday, where he cast the U.S., Britain and other allies in Europe as the world's "greatest catalysts for global action." He planned to echo a similar theme in his discussions with G-8 partners on the recent Arab uprisings and argue that the political protesters in the Middle East and North Africa share their democratic values.

Obama will also hold one-on-one meetings with Sarkozy and Japanese Prime Minister Naoto Kan, the first between the two leaders since the March earthquake and tsunami in northeast Japan that sparked fears of a nuclear meltdown at the damaged Fukushima plant.

The G-8 comprises the U.S., Britain, France, Germany, Italy, Canada, Russia and Japan. The European Union is also represented.

Interim prime ministers from Tunisia and Egypt, where longtime leaders were pushed out of power earlier this year, will join the summit Friday for a special session aimed at identifying their nations' most critical needs as they move toward elections. U.S. officials have said other Arab countries that embark on democratic transitions could also receive financial help.

In a letter to G-8 leaders Tuesday, Secretary of State Hillary Rodham Clinton and Treasury Secretary Timothy Geithner urged the summit partners to help Egypt swap its debt for investments in job creation.

While the U.S. is holding up Tunisia and Egypt as the most successful models to emerge from the Arab unrest thus far, both face significant obstacles on their paths toward democracy. Tunisia has imposed periodic curfews and detained about 1,400 people in continued protests, and in Egypt, sectarian violence has broken out, with Muslims and Coptic Christians clashing in the streets.

Obama will also face questions at the summit about the NATO-led bombing campaign in Libya. Obama said Wednesday that the operation has no clear end date, though he contended it ultimately would be successful in stopping Moammar Gadhafi's attacks on civilians.

Also likely to be discussed are the U.S. troop drawdown plan in Afghanistan, Obama's renewed push for Middle East peace and the continued steps the world's leading economies are taking to recover from the global downturn.

After the summit wraps up Friday afternoon, Obama was to travel to Poland, the last stop on his four-country, six-day tour of Europe that began Monday in Ireland.