Four months later, just last week, Russian President Vladimir Putin announced that he is mobilizing 300,000 more troops against Ukraine.
In a new interview, Zelenska told ABC News' Amy Robach that the new developments are upsetting, especially "when the whole world wants this war to be over.”
"When the whole world wants this war to be over, they continue to recruit soldiers for their army," said Zelenska, who spoke with Robach through a translator. "Of course, we are concerned about this. We are worried, and this is a bad sign for the whole world."
Zelenska said though she feels like Ukraine will continue to persevere in the face of conflict.
"The main difference between our army and the Russian army is that we really know what we are fighting for," she said.
Zelenska's husband, Ukraine's President Volodymyr Zelensky, warned last week in a recorded address to the United Nations General Assembly that Moscow was trying to wait his fighters out.
Zelenska attended the United Nations General Assembly in-person in New York City, where she spoke to Robach.
An independent panel of legal experts for the U.N. recently found that wars crimes have been committed in Ukraine.
In March, Secretary of State Antony Blinken announced that the State Department made a formal assessment that Russian forces have committed war crimes in the country.
Zelenska said she wasn't surprised by the U.N. report but is glad the crimes are internationally recognized now.
"On the one hand, it's horrible news, but it's the news that we knew about already," she said. "On the other hand, it's great news because finally the world can see that this is a total crime, that this is a war against humanity and humankind."
In English, Zelenska directly addressed the American people, saying support from the United States is "crucial."
"It's not war between Ukraine and Russia. It's war for values of all the world. A war for freedom, for human rights, for all that we love, all of the people of the world," she said. "And that's exactly what Ukrainians are fighting for now. So don't stop your support. It's very important for us."
Zelenska recently started a foundation to help Ukrainians recover from the devastating effects of the war with Russia.
She said the foundation is focused on three areas: Education, medicine and humanitarian aid.
"Our main goal is to help as many people as possible to return home," said Zelenska. "For them to be able to return, we need to restore hospitals, schools ... We need to rebuild their homes."