In a sign of a blossoming friendship, Russian President Vladimir Putin has given visiting Greek Prime Minister Alexis Tsipras an ancient Greek icon stolen by Nazis during the German occupation of Greece as the two countries mulled a series of economic projects.

Greece's international creditors are watching Tsipras' visit to Russia with concern amid speculation that Greece might seek aid from Russia, as a bargaining chip with Western creditors.

Putin's spokesman Dmitry Peskov said Putin presented the icon depicting St. Nicholas and St. Spyridon to Tsipras following Wednesday's talks at the Kremlin. He said in remarks carried by Russian news agencies that the icon was stolen by a Nazi officer when Greece was under German occupation in the Second World War, and was recently bought by an unidentified Russian man from the officer's descendants.

Speaking Thursday, Tsipras reaffirmed his opposition to Western sanctions slapped on Russia last year and said his government helped block proposals to strengthen the sanctions.

"Greece could become a bridge between the EU and Russia," he said.

Both he and Putin rejected, however, allegations that they were trying to weaken the European Union's united front on Russia's actions in Ukraine.

Speaking to students, Tsipras said he and Putin have found a way to resume Greek agricultural exports, which were blocked last year under Russia's ban on Western food in retaliation to the EU sanctions. Putin said Wednesday it could be done by setting up joint ventures.

Tsipras also confirmed the two countries have agreed to look into the possibility of extending a Russian gas pipeline to Greece and encourage Russian companies' participation in the privatization of Greek industry.