Leading a crowd of thousands in chants of "Russia, Russia", President Vladimir Putin issued a brief rallying cry during a stadium concert in Moscow to support the country's invasion of Ukraine.

The rally marked a year of the war as well as Defender of the Fatherland Day, a holiday celebrating Russia's veterans.

 "They fight heroically, courageously, bravely. We are proud of them," Putin said of the forces in Ukraine, which he referred to as Russia's "historical frontiers".

The Kremlin casts the war as a "special military operation" to protect Russia's own security in what it sees as an existential confrontation with the West.

"When we are together, we have no equal. To the unity of the Russian people," Mr Putin said.

Mr Putin only spoke for a couple of minutes before Russia's national anthem played and he exited the stage.

It is the third time the Russian president has attended a mass gathering in support of his war in Ukraine, which he launched almost a year ago.

Tens of thousands of people packed into Moscow's Luzhniki Stadium, which hosted the football World Cup final in 2018, waving Russian flags and listening to patriotic songs and military demonstrations before Mr Putin arrived.

A man trumpeted as a hero of Mariupol was celebrated on stage, surrounded by children who, the host of the event said, he rescued from the town.

The UN has voiced concerns that Russian forces have abducted children from besieged areas like Mariupol and put them in the care of Russian families.

The Twitter account of Novaya Gazeta, a Russian media outlet that asserts itself as free from censorship, shared images from outside the venue of pop-up tents offering samples of military rations and classes in crafting ammunition for rally-goers.

Advertisements ahead of the rally, which circulated on Telegram, promised a payment of 500 rubles ($9.77) to those who attended.

Long table policy dropped for Wang Yi

Prior to attending the rally, Mr Putin met with Chinese Foreign Minister Wang Yi at the Kremlin.

Mr Putin hailed ties between the two countries, saying cooperation in the face of global tensions "is particularly important for stabilising the international situation."

A time of crisis required Russia and China "to continuously deepen our comprehensive strategic partnership", Mr Wang agreed.

The relationship between China and Russia, Mr Wang said through an interpreter, was not directed against any third party but equally would "not succumb to pressure from third parties" – a nod to both nations tense relationships with the United States.

The growing friendship between Russia and China was not only symbolised in speech.

Mr Putin is well known for his excessively spaced meetings, in which he would sit at one end of a long, white, oval table and his guest at the other.

Security has been a particular concern for Mr Putin recently – his defence minister was shunted to the end of the long table at their last meeting — and guards posted around the Russian president were noticeably lacking firearms when he ventured out of Moscow to Volgograd earlier this month.

This time, however, Mr Putin and Mr Wang sat opposite each other in the narrow middle of the table, a clear symbol of Mr Putin's trust in the Chinese regime.

Due to sanctions imposed on Russia by the West, China has increasingly become an important trading partner for Russia.

China is Russia's largest buyer of oil, one of the key sources of revenues for the Moscow regime.

'Big mistake', says Biden

US President Joe Biden continued his tour of Poland on Wednesday, meeting with leaders from the Bucharest Nine, a collection of nations in the most eastern parts of the NATO alliance that came together in response to Mr Putin's 2014 annexation of Crimea from Ukraine.

In his first public appearance since Mr Putin announced (and both houses of government approved) Russia's suspension of the New START nuclear arms control treaty overnight, Mr Biden described the move as a "big mistake".

As the war in Ukraine drags on, the Bucharest Nine countries' anxieties have remained heightened.

Many worry Russia could take military action against them next if they're successful in Ukraine.

The alliance includes Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia.

Addressing concerns of the NATO members that they could be next, Mr Biden pledged America's commitment to the treaty.

"As NATO's eastern flank, you are the frontline of our collective defence," Mr Biden said.

The US President arrived in the Polish capital Warsaw late on Monday after a surprise visit to Kyiv just days ahead of the anniversary of Russia's invasion of Ukraine on Friday.

ABC/wires