Vladimir Putin and Xi Jinping have deepened their alliance during Russia's offensive on Ukraine, with the two men seeking to align their positions and often referring to each other as "dear" friends.

Xi has "timed his next visit to Moscow to coincide with events marking victory in the Great Patriotic War on May 9", Russian Foreign Minister Sergei Lavrov told lawmakers on Wednesday.

Putin has elevated the Soviet Union's victory over Nazi Germany in what Russia calls the "Great Patriotic War" to one of Russia's most important national holidays, marked by a giant military parade on Moscow's Red Square.

Putin will also visit China at the end of August and beginning of September "in conjunction with the 80th anniversary of victory over Japanese militarism at the end of the World War II", Lavrov said.

Besides Xi, Putin has invited US President Donald Trump to the May 9 parade in Moscow.