WARSAW/MOSCOW: U.S. President Joe Biden and Russian President Vladimir Putin have been sparring verbally, presenting starkly different views of the world and the Ukraine war, Biden promising to defend democracies and Putin asserting the West was a threat to Russia.

In speeches just hours apart on Tuesday, Putin in Moscow delivered a warning to the West over Ukraine by suspending its last major nuclear arms control treaty with the United States and Biden in Warsaw proclaimed untiring support for Ukraine, which was invaded by Russian forces nearly a year ago on Feb. 24.

"When Russia invaded, it wasn’t just Ukraine being tested. The whole world faced a test for the ages," Biden said in the Royal Castle of Warsaw, the day after he made a secretive surprise visit to the Ukrainian capital Kyiv.

Challenged to respond to the invasion, Biden said the United States and its NATO allies replied: "Yes, we would stand up for sovereignty. And we did. Yes, we would stand up for the right of people to live free from aggression. And we did."

"And we would stand up for democracy. And we did," he said.

Biden went on to say that "there should be no doubt: Our support for Ukraine will not waver, NATO will not be divided, and we will not tire."

NUCLEAR TREATY

Putin, in an earlier speech to Russia's military and political elite, accused the United States of turning the war into a global conflict and announced the suspension of Russia's participation in the New START (Strategic Arms Reduction Treaty). The foreign ministry later said Moscow intended to continue abiding by the restrictions outlined in the treaty on the number of nuclear warheads it could have deployed.

"The elites of the West do not hide their purpose. But they also cannot fail to realise that it is impossible to defeat Russia on the battlefield," Putin said.

"They intend to transform a local conflict into a phase of global confrontation," he said. "This is exactly how we understand it all and we will react accordingly, because in this case we are talking about the existence of our country."

Biden rejected Russia's assertion that Western allies were seeking to control or destroy Russia. He did, however, accuse Russia of crimes against humanity such as targeting civilians and rape. Moscow has denied previous allegations by Ukraine and its allies of war crimes and targeting civilians.

REACTION TO PUTIN

U.S. Secretary of State Antony Blinken called Putin's move "deeply unfortunate and irresponsible". NATO Secretary-General Jens Stoltenberg said it made the world a more dangerous place, and urged Putin to reconsider.

China's U.N. Ambassador Zhang Jun told reporters that the New START treaty and other instruments are important for the global security architecture, adding that "on these important issues the parties concerned should continue to negotiate with each other in finding a good solution".

Under the treaty that expires in 2026, the United States and Russia may physically check the other's nuclear arsenal, although tensions over Ukraine had already brought inspections to a halt.

NATO allies and other supporters have sent Ukraine tens of billions of dollars worth of war weaponry and ammunition, with modern battle tanks promised and some mulling President Volodymyr Zelenskiy's appeals for fighter jets and longer-range missiles.

Russia suffered three major battlefield reverses in Ukraine last year but still controls around a fifth of the country and appears to be making progress in eastern provinces bordering Russia.

Near Bakhmut, the focal point of Russian advances in the eastern region of Donetsk, 18 towns and villages came under fire, the General Staff of the Ukrainian Armed Forces said in a statement on Tuesday night.

The Russian defence ministry said its troops had made a 2.5 km (1.5 miles) advance towards the city of Bakhmut, seen by the Kremlin as a main staging post in capturing other towns further west in Donetsk region.

"It is very important that despite great pressure on our forces, the front line has undergone no change," Ukraine's Zelenskiy said in a nightly video address.

Outspoken Russian mercenary chief Yevgeny Prigozhin chastised military leaders, accusing them of depriving his Wagner fighters of munitions in what he called a treasonous attempt to destroy his private military company. The defence ministry rejected his initial accusations about blocking ammunition as "absolutely untrue".

Reuters was not able to verify battlefield reports.

The biggest land war in Europe since World War Two has displaced millions, left Ukrainian cities, towns and villages in ruins and disrupted the global economy. More than 8,000 civilians have been recorded killed, the U.N. human rights office said, adding thousands more were thought to have died.

Meanwhile, investigations by Denmark, Germany and Sweden into explosions last September on the Nord Stream gas pipelines have not yet concluded, the three countries said on Tuesday as the U.N. Security Council met to discuss the case. The pipelines connecting Russia and Germany spewed gas into the Baltic Sea and worsened a European energy shortage.