Poland announced Friday that it has provided Ukraine with its first Leopard tanks to aid the fight against Russia.

"The Leopard tanks will definitely stand up well in your formation on the battlefield. They will work great," Polish Prime Minister Mateusz Morawiecki told Ukrainian President Volodymyr Zelenskyy during a visit to Kyiv to mark the one-year anniversary of Russia's full-scale invasion.

Poland delivered four Leopard 2A4s -- a model of the latest version of the German main battle tank -- to Ukraine, with more expected to be on the way, according to Morawiecki.

"We will also soon hand over more and we urge our partners from the European Union and NATO to do the same," Morawiecki said.

-ABC News' Joe Simonetti

Ukrainian Foreign Minister Dmytro Kuleba said Friday that his country will do "whatever it takes" to defeat the Russian invaders.

"This war has no timeline. It has only [one] result in the end and that's victory, because we stand for the right cause," Kuleba told ABC News’ George Stephanopoulos during an interview on "Good Morning America."

"We defend ourselves. We are liberating our territory with generous support of many countries of the world, with the United States being at the top of it," he added. "I want to convey the words of gratitude from the people of Ukraine to the people of America for standing by us in this very just struggle for freedom and peace."

Kuleba noted that "ammunition, tanks, long-range missiles, planes" are the "most-wanted weapons" on Ukraine's list.

"I have no doubt that we will prevail," he said. "But, you know, for David to be able to defeat Goliath, David needs a sling. And all of these weapons, it's all about this sling that will help us to win."

Kuleba said Ukrainians are fighting for "territorial integrity."

"If you are attacked, you have to fight. You have to take up the fight and defend your country," he added. "And this is the feeling that drives us through all of this endless suffering."

When asked whether there's any kind of peace proposal that could be accepted by both sides, Kuleba said: "As of now, we are irreconcilable."

"Because while we defend our territory, [Russian President Vladimir Putin] wants to grab our territory. While we want accountability for numerous atrocities committed by the Russian army in Ukraine, Putin wants to escape responsibility," he explained. "This aggression of Russia will go down in textbooks as the most apparent case of aggression in modern history. So the truth is on our side and this is why we feel so empowered to fight and to win."

4:46

Ukrainian foreign minister Dmytro Kuleba talks 1-year anniversary of war with Russia

Speaking to ABC News' George Stephanopoulos on "Good Morning America," U.S. Secretary of State Antony Blinken discussed where things stand in the Russia-Ukraine war on Friday, one year after it began.

"Ukraine is still standing, it remains free, it remains independent," Blinken said. "Putin's first objective was to erase Ukraine from the map, to erase its identity, to absorb it into Russia. That has failed and will never succeed."

"Now, there's a fierce battle going on for the territory that Russia has seized," he added. "Ukraine's gotten about 50% of what Russia's taken since last February and now, there's a fight for the rest."

When asked how long Ukraine can hold on, with its economy devastated and Russian President Vladimir Putin seemingly preparing for a long war, Blinken said he thinks "the Ukrainians are the ones who are going to fight to the finish."

"There's one big difference: The Ukrainians are fighting for their country, for their land, for their future; the Russians are not," he noted. "And at the end of the day, assuming the support continues from so many countries around the world -- material support, military, economic, humanitarian -- Ukraine will succeed."

Blinken said it's "hard to predict" when the war will end.

"No one wants peace more than the Ukrainians, but it has to be a just and durable peace," he added. "Just in terms of reflecting the basic principles that are at the heart of the U.N. Charter, which is territorial integrity of countries, their sovereignty. And durable in the sense that wherever it lands, we don't want it to land in place where Russia can simply repeat the exercise a year or two or five years later."

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Sec. Blinken talks 1-year anniversary of Russian invasion of Ukraine

U.S. Secretary of State Antony Blinken warned Friday that China is "actively thinking about" providing lethal assistance to Russian forces in war-torn Ukraine.

"We're very concerned that they're thinking about it. Up until now, Chinese companies have provided non-lethal support," Blinken told ABC News' George Stephanopoulos during an interview on "Good Morning America."

"From Day One, President Biden warned President Xi not to provide material lethal assistance to Russia for use against Ukraine or to engage in the systematic evasion of sanctions. And the information we have suggests that they’re now actively thinking about it, which is why we've been public about warning them not to," he added. "It could make a material difference in Russia's capacity on the ground at a time when we want to bring this war to an end, not add fuel to the fire and have it continue."

The U.S. government has "shared a lot of information with other countries, with allies and partners," regarding the fact that China is now considering lethal assistance, according to Blinken.

"We always have to get the balance right between making sure that we're protecting the way we get our information and releasing it," he said. "But we thought it was really important to make clear that China's looking at this. And what they're hearing not just from us but from many other countries around the world is: Don't do it."

The Chinese Ministry of Foreign Affairs released a position paper on Friday, calling for a ceasefire between Russia and Ukraine, the resumption of peace talks, an end to unilateral sanctions and the consideration of sovereignty, territorial integrity and security concerns of all countries. Blinken told ABC News that the U.S. government is "taking a look at it."

"No one wants peace more than the Ukrainians and any proposal that can advance peace is something that's worth looking at," he said. "But, you know, there are 12 points in the Chinese plan. If they were serious about the first one, sovereignty, then this war could end tomorrow."

"China's been trying to have it both ways," he added. "It's on the one hand trying to present itself publicly as neutral and seeking peace, while at the same time it is talking up Russia's false narrative about the war, it is, as I said, providing non-lethal assistance to its companies and now contemplating lethal assistance."

4:14

Sec. Blinken talks 1-year anniversary of Russian invasion of Ukraine

A 26-year-old U.S. Marine Corps veteran was killed in a mortar strike last month in Ukraine while working to evacuate civilians, his family confirmed to ABC News this week.

Cooper Andrews died on April 19 in the Bakhmut area, his cousin Willow Pastard, who is speaking on his family's behalf, told ABC News.

The State Department announced Monday that an American citizen died in Ukraine, though did not provide more details or an identity "out of respect for the family's privacy during this difficult time."

"We are in touch with the family and providing all possible consular assistance," a spokesperson for the agency said in a statement.

At least nine deaths of U.S. citizens who have volunteered to fight in Ukraine have been officially reported since the war began last year, according to the State Department.

-ABC News' Shannon Crawford