Russian President Vladimir Putin has memorialized victims of World War Two on a visit to St. Petersburg, the site of a fierce battle against Nazi Germany.

During the war, the Nazis sieged the city, then called Leningrad, for about 900 days from September 1941. Several hundred thousand people died in the blockade.

A ceremony was held in the second-largest Russian city on Wednesday to mark exactly 80 years since the Soviet military broke through the siege, leading to complete liberation of the city the following year.

Putin laid flowers at a monument and a communal cemetery in the city, where his father fought during the war.

He then planned to meet representatives of groups of veterans and patriots, and visit a munitions factory.

Amid his country's invasion of Ukraine, Putin decided to increase the total number of Russian soldiers to about 1.15 million last August.

Defense Minister Sergei Shoigu on Tuesday disclosed that Putin decided to further expand the number to 1.5 million.

A Russian presidential office spokesperson called the decision a response to a proxy war waged by the United States and its Western allies.

Putin apparently aims to stress that he intends to continue the invasion in defiance of international criticism by appealing to the people's patriotic sentiment.