Dmitry Medvedev was set to meet with four Western leaders Monday during a summit of industrialized nations, his biggest international forum since he took over as Russia's president from his patron, Vladimir Putin. Medvedev was holding separate talks with U.S. President George W. Bush, German Chancellor Angela Merkel, French President Nicolas Sarkozy and British Prime Minister Gordon Brown on the sidelines of the summit of the Group of Eight economic powers, the Associated Press reported. After the meeting with Bush, a top Medvedev aide emphasized the positive trend in Russian-U.S. relations but said the United States has failed to ease Russia's concerns about its plans for a European-based missile shield, a major bone of contention. «There is no real progress,» Sergei Prikhodko said. He said Medvedev warned Bush that deploying interceptors for the system in the ex-Soviet republic of Lithuania if talks with Poland fail «would be absolutely unacceptable for the Russian Federation. » Prikhodko said the talks were «exclusively well-intentioned, constructive and open, but at times critical.» He said Medvedev believes «the overall balance of Russian-American relations is without a doubt positive.» The three-day summit and a slew of one-on-one meetings will test Medvedev's diplomatic dexterity two months after his inauguration as president. «I found him to be a smart guy who understood the issues very well,» Bush said of Medvedev. «But I'm not surprised. After all, he has been very close to foreign policy issues up until his ascendancy to the presidency.»