Ukraine has hailed decisions by the US and Germany to supply modern battle tanks as a “historic day” on the path to victory against Russia.

US President Joe Biden on Thursday morning (Australian time) promised 31 Abrams tanks, which he said were “the most capable in the world”.

It came hours after Germany finally agreed to allow its Leopard 2 tanks to be used in the war after weeks of international pressure.

Ukraine President Volodymyr Zelensky thanked Mr Biden for his “powerful decision”.

“It’s an important step on the path to victory. Today the free world is united as never before for a common goal – liberation of Ukraine. We’re moving forward,” Mr Zelesnky wrote on Twitter.

However Russia has reacted angrily, saying the “extremely dangerous” decision to arm Ukraine with battle tanks was an escalation that would take the war to a “new level”.

Tweet from @ZelenskyyUa

The US had previously stated it would not be supplying Ukraine with Abrams tanks, despite months of pleading.

In an apparent stand-off, Berlin said it would also not allow its German-made Leopard tanks to go to Ukraine unless the US made a similar move.

When asked whether America’s new decision came under pressure from Germany, Mr Biden said: “Germany didn’t force me to change my mind.”

German Chancellor Olaf Scholz is seeking to reassure his citizens – who were concerned about antagonising Russia – that it was the right decision, saying “trust me”.

Germany will send an initial company of 14 Leopard 2 tanks from its own stocks, and also approve shipments by allies who field them, with the aim of supplying Ukraine with two full battalions.

A battalion normally comprises three to four companies.

Kyiv had for months been calling for Western main battle tanks that would give its forces the firepower, protection and mobility to break through Russian defensive lines and swoop through territory occupied by the invaders.

Kremlin spokesman Dmitry Peskov said any US tanks sent to Ukraine would “burn like all the rest”.

Twenty armies worldwide field Leopards, which Germany has made in their thousands.

Poland and Finland have already pledged them once Berlin agrees, and several other countries are expected to follow swiftly. Britain has already offered a company of its comparable Challengers and France is considering sending its Leclercs.

Moscow says supplies of modern offensive weaponry to Ukraine will only prolong the war and postpone what it says will be its inevitable victory.

Anatoly Antonov, Russia’s ambassador in Washington, said deliveries of US battle tanks would be a “another blatant provocation”.

“It is obvious that Washington is purposefully trying to inflict a strategic defeat on us,” Mr Antonov said on the embassy’s Telegram messaging channel.

In the past week, Russia has ramped up its threats, with Putin ally Dmitry Medvedev saying openly that a nuclear power that faced defeat could use nuclear weapons.

Western officials who support sending the tanks have dismissed Moscow’s threats as bluster, arguing that Russia is already waging war at full tilt in Ukraine, and has been deterred from attacking NATO or using nuclear arms.

Apart from its military significance, the decision to send tanks removes one of the last taboos in Western support: against providing weapons that have a mainly offensive rather than defensive purpose.

Just last week, allies pledged billions of dollars’ worth of fresh military aid but stopped short of sending the tanks, with some politicians in Germany notably wary of provoking Moscow.

In the 11 months since it invaded, Russia has killed thousands of civilians, forced millions from their homes and reduced entire cities to rubble.

It says its “special military operation” was necessary to stem a security threat arising from Ukraine’s ties to the West, which it now portrays as seeking to destroy it. Kyiv and its Western allies say Ukraine never threatened Russia, and the invasion is a war of aggression to subdue its neighbour and seize land.

Ukraine defeated Russia’s troops on the outskirts of Kyiv last year and later drove them out of swathes of occupied land.

But Moscow still occupies around a sixth of Ukraine, which it has declared part of Russia forever. Ukraine says it will not stop fighting until it recaptures all its territory, and the only way to secure peace is for allies to help it win.

The front line has been largely frozen in place for two months despite heavy losses on both sides, with both believed to be planning offensives for the northern spring.

Mr Zelensky said Russia was intensifying its push toward Bakhmut, an industrial town in eastern Ukraine where thousands of troops have been killed in months of trench battles that both sides refer to as a meat grinder.

The Russian-installed governor of Ukraine’s Donetsk region said units of Russia’s Wagner contract militia were moving forward inside Bakhmut.

“Fighting is already taking place in the outskirts and in neighbourhoods that until very recently were held by the enemy,” TASS news agency quoted Denis Pushilin as saying.

Reuters could not verify the situation there.