Ukrainian President Volodymyr Zelenskyy criticised European Union leaders, saying that sanctions and support for Ukraine came "a little late".
"You have applied sanctions. We are grateful. These are powerful steps but it was a little late," Zelenskyy said in an address to the EU council.
"If it had been preventive, Russia would not have gone to war. At least no one knows for sure. There was a chance," he added.
He commended Germany for blocking Nord Stream 2 but again reiterated that the move could have been more timely.
The Ukrainian president also reiterated a plea to join the European Union, begging leaders not to "be late" on letting the country in.
The EU summit was the third major meeting of western leaders on Thursday to discuss Ukraine one month after Russia began its invasion of the neighbouring country.
Russians and Ukrainians exchanged prisoners on Thursday, according to the Ukrainian deputy prime minister and the Russian human rights delegate.
US President Joe Biden will travel to Poland on Friday close to the border with Ukraine as the country hosts more than two million refugees.
In the month since the war began, more than 3.6 million people have fled the war in Ukraine. Most of them have fled to neighbouring Poland, which has taken in over two million refugees.
Millions of Ukrainians are also internally displaced within the country as heavy fighting and shelling forces people to flee several cities.
More than half of Ukraine's child population is displaced, according to the UN Children's Fund, UNICEF.
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