Espionage under Russian law can be punishable by up to 20 years in jail.

Russian officials say their forces are still capturing ground in street-by-street fighting inside Bakhmut.

He opposes any notion of Russian and Belarusian athletes competing as neutrals with no use of flags or anthems allowed.

Alexei Moskalyov has been separated from his 13-year-old daughter Masha since he was placed under house arrest at the start of this month and she was moved to a children's home.

The battle for Bakhmut, a mining city in the Donetsk region, has been the focus of Moscow's war in Ukraine for months, with both sides describing the fighting there as a 'meat grinder'.

Front lines in Ukraine have barely budged for more than four months despite a Russian winter offensive using hundreds of thousands of freshly called-up reservists and convicts recruited as mercenaries from jail.

Putin likened his plans to the US stationing its weapons in Europe, and said Russia would not be transferring control of the weapons to Belarus.

Moscow and Kyiv have accused each other of mistreating prisoners of war since Russian President Vladimir Putin invaded a year ago.

The remarks are the strongest indication yet from Kyiv that it is close to shifting tactics, having absorbed Russia's onslaught through a brutal winter.

Dmitry Medvedev, who served as president between 2008 and 2012, has made increasingly hawkish speeches since Putin sent troops to Ukraine, repeatedly issuing nuclear threats.

Relations between Russia and the US, long strained, have worsened even further since Russia's invasion of Ukraine last year.

China has promoted itself as a neutral peacemaker, proposing a plan for Ukraine last month which the West largely dismissed as vague at best, and at worst a ploy to buy time for Putin to regroup his forces.