(Reuters) -Russian President Vladimir Putin on Friday denied Moscow was preventing Ukrainian ports from exporting grain and said the best solution would be to ship it through Belarus, as long as sanctions on that country were lifted. Putin, saying reports of a Russian export ban were “a bluff”, told national television that Western nations were trying to cover up their own policy mistakes by blaming Russia for problems on the global food market. Russia’s army has seized much of Ukraine’s southern coastline and its warships control access to the country’s Black Sea ports. Moscow has blamed Ukra…