Ukraine's President Volodymyr Zelensky has made an urgent appeal for more weapons to avoid a "catastrophic" situation in Europe.
An "artificial deficit of weapons" will only help Russia, Mr Zelensky told an international conference in Germany.
Ukrainian troops have been running out of ammunition as vital US support has been held up by supporters of former President Donald Trump in Congress.
Mr Zelensky said he was prepared to tour the front lines with Mr Trump.
"If Mr Trump will come, I am ready to go with him to the front line. What does it mean, the real war, not Instagram, the real war," the Ukrainian president said.
Mr Zelensky was speaking at the Munich Security Conference - a gathering of world leaders and senior defence officials - ahead of the two-year anniversary of Russia's full-scale invasion of Ukraine.
The speech also coincided with Ukrainian troops withdrawing from Avdiivka, a key city in eastern Ukraine, marking one of Russia's biggest military victories for months.
Acknowledging the setback, Mr Zelensky told the Munich gathering that Ukrainian efforts were "limited only by the sufficiency and length of range of our strength".
"Keeping Ukraine in the artificial deficits of weapons, particularly in deficit of artillery and long-range capabilities allows Putin to adapt to the current intensity of the war," he said.
"Ukrainians have proven that we can force Russia to retreat," he said. "We can get our land back."
He went on to warn that the Russian leader would make the next few years "catastrophic" for many more countries if the Western world did not stand up to him.
"Do not ask Ukraine when the war will end. Ask yourself, why is Putin still able to continue it?" Mr Zelensky told the conference.
Ukraine is critically dependent on weapons supplies from the US and other Western allies to keep fighting Russia - a much bigger military force with an abundance of artillery ammunition.
UK Foreign Secretary David Cameron said help for Ukraine from the UK, the EU and the US would make a "real difference" to the fight against Russia.
Earlier this week, the US Senate approved a $95bn (£75bn) foreign aid package - including $60bn for Ukraine - after months of political wrangling, but it faces an uphill battle in the House of Representatives, where members of the Republican Party who are loyal to Mr Trump seem unwilling to pass the measure.
Outgoing Dutch Prime Minister Mark Rutte told the Munich conference Europe should help Ukraine more because it was in its interests, and stop "all that whining and moaning about Trump".
German Chancellor Olaf Scholtz had a similar message for the conference.
"Irrelevant of the election results on this or the other side of the Atlantic, one thing is clear: we Europeans must take much more care of our own security, now and in the future."