President Volodymyr Zelensky has told Ukrainians they have "withstood the blow" of Russia's invasion as he urged citizens to continue fighting.
In an impassioned speech delivered from Kyiv on Saturday night, Mr Zelensky told the country that the time has come for them to launch a fightback.
"You need to go out and drive this evil out of our cities," he said.
The rallying cry came alongside a plea to US President Joe Biden to source more combat jets for Ukraine.
US officials are believed to be in discussions with political leaders in Poland over the possibility of Warsaw providing Ukraine with a number of MiG fighter jets.
Poland has been slowly phasing the Soviet-era fighter out of use - and officials are understood to be weighing whether to provide them to Ukraine, where pilots are not trained to fly Western-made jets.
Some reports suggest they could be exchanged for new US-sponsored replacements.
The Russian invasion of Ukraine has entered its 11th day, with some experts suggesting the invasion may have stalled in places - despite President Vladimir Putin's insistence on Saturday that the operation is "going to plan."
While fighting has continued in many parts of the country, Moscow's forces have only captured one major Ukrainian city, Kherson - though it has made other key advances, such as seizing the Zaporizhzhia nuclear power plant on Friday.
Much of Russia's military has so far underperformed in Ukraine.
Prior to the invasion, it was assumed the army had undergone a radical re-haul, reorganising itself into so-called "Battalion Tactical Groups". These units of 800 to 1,000 men would operate in close coordination with tanks, drones and multiple-launch rocket systems to deliver a multi-faceted punch to the enemy.
But it hasn't worked out like that.
Russian commanders, especially in the north, have manifestly failed to make full use of this modern kind of warfare.
Their vehicles have also suffered mechanical breakdowns and they appear to have underestimated the strength of Ukrainian resistance, losing large numbers of men and equipment.
So now, as grimly predicted, the gloves have come off.
Russian military tactics have reverted to a crude but tried and tested doctrine: encircle a city, pummel it with airstrikes, tank and artillery fire, and break the morale of both its defenders and those simply trying to survive.
International condemnation of the mounting civilian casualties will not bother President Putin. He's made it abundantly clear he has no intention of calling off this invasion.
Outside the capital of Kyiv, a massive convoy stretching over 40 miles (64km) remains stalled outside the city and Ukrainian defence officials say they have been hitting selected targets within the convoy where they can. Elsewhere:
The head of the UN's refugee agency told Reuters that the number of refugees fleeing the Russian invasion could rise to 1.5 million by the end of the weekend.
"This is the fastest moving refugee crisis we have seen in Europe since the end of World War Two," UNHCR head Filippo Grandi said.
As fighting rumbles on in Ukraine, Western sanctions continue to hammer the Russian economy.
On Saturday night, the payments giants Visa and Mastercard both announced that they will withdraw their services from Russia, with Visa's chief executive Al Kelly saying in a statement that the company had been "compelled to act following Russia's unprovoked invasion of Ukraine, and the unacceptable events that we have witnessed".
The move means Russian banks will no longer be supported by the companies' networks, and any cards issued outside of the country will stop working at Russian merchants or ATMs.
But Sberbank, the country's largest lender, emphasised that Russians will be able to withdraw cash, make transfers, and pay both in offline stores and Russian internet stores, because transactions in the country pass through the domestic National Payment Card System, which does not depend on foreign payment systems.
Meanwhile, with further economic sanctions under discussion in Washington and Brussels, President Putin has warned Western leaders that the economic punishments being heaped on Russia are "akin to a declaration of war".
Mr Putin also cautioned Ukrainian leaders that continued resistance to the Russian invasion could call "into question the future of Ukrainian statehood".
Despite the ominous warning, Mr Putin met Israeli Prime Minister Naftali Bennett in Moscow on Saturday, his first meeting with a Western leader since he launched his invasion of Ukraine.
Mr Bennett, who is said to have a friendly relationship with the 69-year-old leader, has previously offered to broker peace talks between Kyiv and Moscow.
Elsewhere, President Biden told Mr Zelensky that he will work with congress to increase US humanitarian and security assistance to Ukraine during a call on Saturday night.
Mr Biden is reported to be seeking a package of $10bn (£7.56bn) in emergency funding to respond to the crisis.
Mr Zelensky had earlier addressed a video meeting of over 300 US lawmakers. US media reported that he urged those present to introduce an oil embargo on Russia and push Eastern European countries to provide Russian-made planes to his country.
White House officials told Politico that the plan is under consideration and that the Biden administration is "working on the capabilities we could provide to backfill Poland if it decided to transfer planes to Ukraine".