In a historic speech to the U.S. Congress, Zelenskyy claims that despite all chances, "Ukraine didn't collapse."

In his first speech to a joint session of the U.S. Congress, Ukrainian President Volodymyr Zelenskyy said his country had persevered through years of war and occupation and had emerged 'stronger than ever.'

'Against all odds, Ukraine didn't fall,' Zelenskyy said in the Wednesday night address. 'We are still standing.'

Zelenskyy, who was elected in a landslide last year on a promise to end the country's long-running war with Russia-backed separatists in the east, said Ukraine had been 'forced to defend our independence and sovereignty in the bloodiest conflict since World War II.'

'More than 13,000 of our soldiers and over 30,000 of our civilians have been killed,' he said. 'But we will never give up. We will never surrender. Because this is not just our war. This is the world's war.'

Zelenskyy said that, despite the odds, Ukraine had made 'tremendous progress' in recent years, including adopting reforms to fight corruption and modernizing its economy.

'I believe that the 21st century will belong to Ukraine,' he said.

Zelenskyy's address came as Ukraine is locked in a tense standoff with Russia over the continued presence of Russian troops in Crimea, which Russia annexed in 2014, and in the eastern regions of Donetsk and Luhansk.

The Ukrainian leader called on the international community to maintain sanctions on Russia until it withdrawal its troops from Ukrainian territory and implements the terms of a peace agreement signed in 2015.

'We cannot allow the world to forget about Crimea,' he said. 'We cannot allow the world to forget about Donbas.'

Zelenskyy also called on the United States to provide Ukraine with 'powerful and effective' military assistance, including lethal weapons, to help it defend itself against Russia.

'I am confident that, together, we will win,' he said.