President Vladimir Putin said on Thursday Russia would not legalize gay marriage as long as he was in the Kremlin.

He made clear he would not allow the traditional notion of mother and father to be subverted by what he called "parent number 1" and "parent number 2".

"As far as 'parent number 1' and 'parent number 2' goes, I've already spoken publicly about this and I'll repeat it again: as long as I'm president this will not happen. There will be dad and mum," Putin said.

During his two decades in power, Putin has closely aligned himself with the Orthodox Church and sought to distance Russia from liberal Western values, including attitudes towards homosexuality and gender fluidity.

He made the comments as he met a state commission to discuss changes to Russia's constitution.

The commission was set up last month after Putin announced sweeping changes to Russia's political system that are widely seen as being designed to help him extend his grip on power after his scheduled departure from office in 2024.

Other proposals have since been put forward and Putin was asked to comment on a proposal to add a line in the constitution defining marriage as a union between a man and a woman.

"We need only to think in what phrases and where to do this," he replied.

In separate comments during the meeting, Putin said he backed an idea to make it unconstitutional for Russia to give away any part of its territory, a move likely to irritate Japan and Ukraine that have land disputes with Moscow.

Russia annexed the peninsula of Crimea from Ukraine in 2014 and has been in a decades-long dispute with Tokyo over ownership of a chain of islands in the Pacific that Moscow seized from Japan at the end of World War Two.

Russia and Japan have been holding talks on the latter dispute which has prevented the countries formally signing a peace treaty after World War Two.

"We have talks under way with our partners on certain questions, but I like the idea itself," Putin said. "So let's instruct the lawyers, ask them to formulate this in the right way."