China, Russia deepen ties as Biden rallies NATO's 'frontline' over Ukraine

However, a day after President Vladimir Putin said Moscow was suspending participation in a nuclear arms reduction treaty with Washington, his deputy foreign minister sought to calm nerves, saying the step did not make a nuclear war more likely.

Within Ukraine, schools took their classes online for the rest of the week for fear of an upsurge in Russian missile attacks a year on from Moscow's Feb. 24 all-out assault, which failed to topple the government and has long been bogged down.

Wang Yi, the highest ranking Chinese official to visit Russia since the countries announced a "no limits" partnership weeks before the invasion, told Putin that Beijing was ready to enhance ties.

A time of crisis called for Russia and China "to continuously deepen our comprehensive strategic partnership", Beijing's top diplomat said.

Putin said he was looking forward to a visit to Moscow by Chinese President Xi Jinping and a deeper partnership.

Xi is expected to make a "peace speech" on Friday, but Kyiv says there can be no talk of peace while Russian troops are in Ukraine.

"This unprovoked and criminal Russian war against Ukraine, Europe and the democratic world must end with the cleansing of the entire Ukrainian land from Russian occupation and solid guarantees of the long-term security for our state, the whole of Europe and the entire world," President Volodymyr Zelenskiy wrote on the Telegram messaging app.

Russia is due to begin military exercises with China in South Africa on Friday and has sent a frigate equipped with new generation hypersonic cruise missiles. A Russian officer said on Wednesday Russia would fire artillery, but not the missiles, whose speed makes them difficult to shoot down.

Russian aggression in Ukraine has changed the security situation in Europe, Polish President Andrzej Duda told the Warsaw meeting of nine eastern NATO members with Biden, who said Washington was committed to defending every inch of the alliance's territory.

"You are the front line of our collective defence," Biden told the summit of countries which joined the Western military alliance after being aligned with Moscow during the Cold War.

Most now count among the strongest supporters of military aid to Ukraine and in a joint declaration called for NATO's enhanced presence on its eastern flank.

NUCLEAR TREATY SUSPENDED

Putin has responded to setbacks in Ukraine with veiled threats to use nuclear weapons and suspended the nuclear arms control treaty on Tuesday, accusing Washington of turning the war into a global conflict by arming Ukraine.

Russia's foreign and defence ministries said later Moscow would still continue abiding by the restrictions outlined in the pact on the number of nuclear warheads it could have deployed and the number of nuclear missile carriers. Russia's lower house of parliament rubber-stamped the move Wednesday.

Tension over Ukraine had already halted mutual inspections of nuclear arsenals envisaged by the treaty, but Biden said that by suspending the treaty, Putin had "made a mistake".

He underlined his support for Kyiv in a surprise visit to war-torn Ukraine on Monday and then rallied NATO allies in Poland, saying the invasion had tested the world but Washington and its allies had shown they would defend democracy.

He rejected Russia's assertion that the West was seeking to control or destroy Russia, and accused Moscow of crimes against humanity such as targeting civilians and rape. Russia denies committing war crimes or deliberately attacking civilians.

NATO allies and other supporters have sent Ukraine tens of billions of dollars worth of arms and ammunition. Since the new year they have promised modern battle tanks, though they have yet to offer Western fighter jets sought by Kyiv.

U.S. Secretary of State Antony Blinken has warned Beijing against supplying weapons to Moscow, prompting anger from China.

Britain has begun to "warm up" its production lines to replace weapons sent to Ukraine and increase production of artillery shells to try to help Kyiv push back Russian forces, defence minister Ben Wallace said.

Speaking in southwest England where British officers are training Ukrainian crews on Challenger-2 tanks, Wallace said Challenger tanks would arrive in Ukraine in "the spring".

FIGHTING

Russia suffered three major battlefield setbacks in Ukraine last year but still holds nearly a fifth of the country. It has launched a massive offensive in recent weeks in the east, so far making only marginal gains despite some heavy losses.

Ukraine's military said Bakhmut city, the focus of Russian advances in the eastern region of Donetsk, came under shelling, along with 20 other settlements in the area.

The governor of the neighbouring Luhansk region, Serhiy Haidai, said Ukraine had repelled intense Russian attacks around Kreminna town further north, destroying several of their tanks.

Two civilians were killed in Russian shelling of the Kherson region in southern Ukraine, and two were wounded in a missile strike on the northeastern city of Kharkiv, officials said.

Reuters was not able to independently verify the reports.