Just as Ukraine is showing signs of making tangible gains in its war with Russia, serious divisions within the Western alliance are jeopardising its forces’ prospects of ultimately declaring victory.
In recent months Ukrainians have defied expectations by securing a number of important territorial gains, including recapturing the cities of Kharkiv in the north and Kherson in the south.
But with Russian President Vladimir Putin said to be planning a new spring offensive to reverse the humiliating losses his forces suffered towards the end of last year, Kyiv is desperately seeking fresh supplies of military equipment to sustain its war effort.
In particular, Ukrainian commanders say they need at least 300 tanks if they are to defend themselves against their Russian occupiers.
But while major Western powers such as the US, Britain, France and Germany have shown themselves willing to provide weaponry that allows Ukraine to defend itself against Russian aggression, they have been less willing to supply equipment, such as tanks and warplanes, that could be used to support offensive operations.
From the outset of the conflict last February, US President Joe Biden and other Western leaders have been anxious to avoid provoking a wider conflict between Russia and the Nato alliance, with concerns that supplying Ukraine with offensive weaponry could spark an escalation.
These concerns have now resulted in tensions developing between Western leaders over how far they should go in responding to Ukrainian President Volodymyr Zelensky’s request for more weaponry.
At the heart of the dispute is an argument over whether to accede to Zelensky’s request for the Western powers to equip the Ukrainian forces with modern battle tanks, which would give them a distinct advantage over Russia’s ageing fleet of Soviet-era T-72 tanks.
Ukraine says Western tanks would give its ground troops the mobility, protection and firepower it needs to break through Russian defensive lines and resume their advance.
"We need tanks. Not 10-20 but several hundred," Zelensky's chief of staff Andriy Yermak wrote on Telegram in late January.
"Our goal is (restoring) the borders of 1991 and punishing the enemy, who will pay for their crimes."
The Ukrainian request has prompted a hesitant response from Western leaders.
In Washington the Biden administration has agreed to provide 50 Bradley Armoured Fighting Vehicles which, while lacking the firepower of a main battle tank, nevertheless have the ability to destroy any Russian tanks it encounters.
France, similarly, has offered to provide its own armoured combat vehicle — the AMX-10 RC.
By contrast other European countries, most notably Britain and Poland, have pledged to provide the Ukrainian forces with hi-end battle tanks: Britain has offered to send 14 Challenger 2 tanks, while Poland has offered to supply its German-made Leopard 2 tank.
The initiative to supply Ukraine with battle tanks has encountered stiff resistance within Germany, where Chancellor Olaf Scholz was reluctant to authorise the transfer of the Leopards to Ukraine.
Poland requires authorisation from Berlin to re-export its tanks, and the German government’s sustained unease before granting approval has caused tensions between countries willing to equip Ukraine with tanks and those who are more cautious.
The disagreement between Western leaders on the issue was very much in evidence at a 20 January summit at Germany’s Ramstein Air Base, held to discuss future weapons deliveries to Ukraine.
It ended with the US and its allies failing to persuade Berlin to drop its opposition to equipping Ukraine with tanks, although it did so later, agreeing to send 14 Leopards and clearing its allies to redeploy theirs.
Before Berlin’s change of heart, Mateusz Morawiecki, the prime minister of Poland, said Chancellor Scholz’s position was “unacceptable” and hinted Warsaw could find a way to export without German permission.
Meanwhile, Poland suggested it and other Nato allies may organise their own “tank alliance” for Ukraine without Germany. Latvia's foreign minister said "there are no good arguments" why the battle tanks could not be provided.
The row has also prompted tensions between Washington and Berlin, with reports that American officials had tense exchanges with their German counterparts.
According to a report in the German newspaper Süddeutsche Zeitung, US National Security Advisor Jake Sullivan read “the riot act” to Jens Plotner, Scholz’s foreign policy advisor, over Berlin’s intransigence.
The fierce disagreements among Western leaders over how best to respond to Ukraine’s request for more weapons will certainly lend encouragement to Moscow, where Putin has long argued that the Western alliance is too weak and divided to provide any meaningful opposition to Russia’s advance into Ukraine.