Putin suspends US nuclear treaty, vows to keep fighting in Ukraine

President Vladimir Putin on Tuesday suspended Moscow's participation in a nuclear arms reduction treaty with Washington during a speech in which he accused the West of escalating the Ukraine conflict.

In his scathing state of the nation address to Russian lawmakers, Putin also vowed that Russia would keep fighting in Ukraine ahead of the first anniversary of the military campaign.

Accusing Western powers of wanting "to be done with us once and for all", he said Russia was "forced" to suspend the New START treaty but would not pull out of the agreement altogether.

The 2010 treaty is the last major US-Russia arms control pact still in force but it has frayed in recent years, with accusations from Washington that Moscow was not complying with it.

Read | US slams 'absurdity' of Putin's anti-West speech

Putin was speaking a day after US President Joe Biden made a surprise visit to Kyiv in which he promised additional arms deliveries for Ukraine, and ahead of a speech by Biden in Warsaw.

Referring to the conflict in Ukraine, Putin said: "step by step, we will carefully and systematically solve the aims that face us".

He said it was "impossible to defeat Russia on the battlefield".

"The responsibility for fuelling the Ukrainian conflict, for its escalation, for the number of victims... lies completely with Western elites," Putin said.

A top US official described as an "absurdity" Putin's accusations that Russia had been threatened by the West as justification for sending troops into Ukraine.

"Nobody is attacking Russia. There's a kind of absurdity in the notion that Russia was under some form of military threat from Ukraine or anyone else," White House National Security Advisor Jake Sullivan told reporters in Warsaw.

Putin also issued a warning to critics within Russia, saying: "Those who have embarked on the path of betrayal of Russia must be held accountable under the law".

Turning to the economy, Putin said sanctions against Russia had not succeeded and were in fact hurting the West by raising energy prices.

"They have not succeeded and will not succeed," he said.

"The Russian economy has proved much more resilient than the West expected."

Russian official data on Monday showed the economy contracted by 2.1 percent last year despite sanctions -- far less than had been expected.

Biden is due to deliver his own speech at around 1630 GMT after talks with Polish President Andrzej Duda, who has been a key advocate for Ukraine within the EU and NATO.

From Warsaw's historic Royal Castle, Biden will "make it clear that the United States will continue to stand with Ukraine... for as long as it takes", according to National Security Council spokesman John Kirby, who spoke to reporters last week.

He will also speak by telephone with the leaders of Britain, France and Italy, the White House has said. German Chancellor Olaf Scholz is due in Washington on March 3.

"You'll hear messages in the president's speech that will certainly resonate with the American people, certainly will resonate with our allies and partners, without question resonate with the Polish people," Kirby said of the Warsaw address.

"I would suspect that you'll hear him messaging Mr Putin as well, as well as the Russian people."

At his meeting with Ukrainian President Volodymyr Zelensky on Monday, Biden pledged "unwavering" US support and some $500 million in ammunition and artillery supplies.

The visit came ahead of the February 24 anniversary of when Putin gave the order for Russian troops to enter Ukraine.

"One year later, Kyiv stands. And Ukraine stands. Democracy stands," Biden said at the Mariinsky Palace, the Ukrainian president's official residence.

When the Kremlin launched the offensive in Ukraine, its so-called "special military operation" was planned to be a rapid conquest leading to capitulation and the installation of a pro-Russian regime.

"Putin thought Ukraine was weak and the West was divided," Biden said Monday. "He thought he could outlast us."

"He's just been plain wrong," he added.

On Tuesday, China said it was "deeply concerned" about the conflict, which it said was "intensifying and even getting out of control".

Foreign Minister Qin Gang said Beijing would "urge the countries concerned to stop adding fuel to the fire as soon as possible, to stop shifting the blame to China", following US claims that Beijing may be considering sending arms to Moscow.

China has sought to position itself as a neutral party, while maintaining close ties with its strategic ally Russia.

China's top diplomat, Wang Yi, is due in Moscow on Tuesday for talks, in his final stop of a European tour.

The Kremlin has said Wang may meet Putin during his visit, according to the state TASS news agency.

According to the latest estimates from Norway, the conflict has wounded or killed 180,000 Russian soldiers and 100,000 Ukrainian troops.

Other Western sources estimate the conflict has caused 150,000 casualties on each side.