But France and Poland appear to be willing to entertain any such request from Ukraine, with Macron telling reporters in The Hague on Monday that “by definition, nothing is excluded” when it comes to military assistance.

In remarks carried on French television before Biden spoke in Washington, Macron stressed any such move would depend on several factors including the need to avoid escalation and assurances that the aircraft would not “touch Russian soil”.

He said Reznikov would also meet his French counterpart Sebastien Lecornu in Paris on Tuesday.

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In Poland on Monday, Prime Minister Mateusz Morawiecki also did not rule out a possible supply of F-16s to neighbouring Ukraine, in response to a question from a reporter before Biden spoke.

Morawiecki said in remarks posted on his website that any such transfer would take place “in complete coordination” with Nato countries.

Andriy Yermak, head of the Ukraine president’s office, noted “positive signals” from Poland and said France “does not exclude” such a move in separate posts on his Telegram channel.

Biden’s comment came shortly after Ukrainian President Volodymyr Zelensky said Russia had begun exacting its revenge for Ukraine’s resistance to its invasion with relentless attacks in the east, where it appeared to be making incremental gains.

Zelensky has warned for weeks that Moscow aims to step up its assault after about two months of virtual stalemate along the front line that stretches across the south and east.

Ukraine won a huge boost last week when Germany and the United States announced plans to provide heavy tanks, ending weeks of diplomatic deadlock on the issue.

02:09

As Western tanks head to Ukraine, the nation’s pilots appeal for US Apache attack helicopters

As Western tanks head to Ukraine, the nation’s pilots appeal for US Apache attack helicopters

While there was no sign of a broader new Russian offensive, the administrator of Russian-controlled parts of Ukraine’s eastern Donetsk province, Denis Pushilin, said Russian troops had secured a foothold in Vuhledar, a coal-mining town whose ruins have been a Ukrainian bastion since the outset of the war.

Pushilin said that despite “huge losses” Ukrainian forces were consolidating positions in industrial facilities.

Pushilin said Ukrainian forces were throwing reinforcements at Bakhmut, Maryinka and Vuhledar, towns running from north to south just west of Donetsk city.

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The Russian state news agency Tass quoted him as saying Russian forces were making advances there, but “not clear-cut, that is, here there is a battle for literally every metre”.

In an intelligence update offering rare battlefield detail, the British ministry said Russia was attacking Vuhledar with a force at least the size of a brigade, a unit normally comprising several thousand troops with a full range of capabilities.

So far, the Russians had likely advanced from the south several hundred metres beyond the Kashlahach River, which it said had marked the front line for months. The small river flows on the edge of the town of Pavlivka, about 2km south of Vuhledar.

Ukrainian military analyst Oleh Zhdanov said Ukraine still controlled Maryinka and Vuhledar, where Russian attacks were less intense on Monday.

Pushilin’s adviser, Yan Gagin, said fighters from Russian mercenary force Wagner had taken partial control of a supply road leading to Bakhmut, a city that has been Moscow’s focus for months.

A day earlier, the head of Wagner said his fighters had secured Blahodatne, a village just north of Bakhmut, although Kyiv said it had repelled assaults on Blahodatne.

In central Zaporizhzhia region and in southern Kherson region, Russian forces shelled more than 40 settlements, Ukraine’s General Staff said. Targets included the city of Kherson, where there were casualties.

The Russians also launched four rocket attacks on Ochakiv in southern Mykolayiv, the army said, on the day Zelensky met the Danish prime minister in Mykolayiv city, to the northeast.

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Zelensky is urging the West to hasten delivery of its promised weapons so Ukraine can go on the offensive, but most of the hundreds of tanks pledged by Western countries are months away from delivery.

With Ukraine’s supplies of artillery munitions heavily depleted, France and Australia announced Monday a deal to jointly produce 155mm shells for Kyiv’s forces.

Meanwhile, in Seoul, Nato Secretary General Jens Stoltenberg asked South Korea to “step up” military support for Ukraine, suggesting it reconsider its policy of not exporting weapons to countries in conflict.

There is an “urgent need for more ammunition,” Stoltenberg said.

British Defence Minister Ben Wallace said the 14 Challenger tanks donated by Britain would be on the front line around April or May, without giving an exact timetable.

Kremlin spokesperson Dmitry Peskov said Western countries supplying arms leads “to Nato countries more and more becoming directly involved in the conflict – but it doesn’t have the potential to change the course of events and will not do so”.

The US-based Institute for the Study of War think-tank said “the West’s failure to provide the necessary materiel” last year was the main reason Kyiv’s advances had halted since November.

The researchers said in a report that Ukraine could still recapture territory once the promised weapons arrive.

The Russian invasion of Ukraine, which Moscow justifies as necessary to protect itself from its neighbour’s ties with the West, has killed tens of thousands of people and driven millions from their homes.

Additional reporting by Agence France-Presse