Ukrainian president Volodymyr Zelensky and his Lithuanian counterpart spoke with students in Poland via video link.
Mr Zelensky is carried out a questions and answers session with the students in Warsaw.
Lithuania's president, Gitanas Nauseda, also made a speech during his appearance.
It comes as Poland became the latest country to pledge to send more Leopard 2 tanks to help Ukraine bolster its defences.
The Polish prime minister, Mateusz Morawiecki, said he will send 14 of the Leopard 2 tanks.
In addition, they will also send 60 of its PT-91 tanks, Polish-made battle tanks.
In response, Mr Zelensky thanked Poland on Twitter for the decision to send them.
"Like 160 years ago we are together, but this time the enemy doesn't stand a chance. Together we will win," he tweeted.
Mr Morawiecki replied: "We were, we are and we will be together."
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