WASHINGTON (AFP) - Ukraine's first lady made an emotional pitch on Wednesday (July 20) to US lawmakers for more weapons to fight Russian invaders, saying she spoke for millions of parents fearing for their children.

Taking a cue from her husband, President Volodymyr Zelensky, who showed graphic images during his virtual appearance before the US Congress, Olena Zelenska - who appeared in person - displayed images of joyful children who were killed or maimed by Russia.

Among them was Liza Dmitrieva, a four-year-old with Down's syndrome pictured in her mother's video happy on her stroller an hour before she was killed by a Russian strike last week in Vinnytsia.

"We want every father and every mother to be able to tell their child, 'Go to sleep peacefully, there will be no more air strikes, no more missile strikes.' Is this too much to wish for?" Zelenska said.

Zelenska, stepping into a more public role after staying sheltered immediately following Russia's Feb 24 invasion, acknowledged it was unusual for a first lady to seek weapons but said it was vital.

Ukraine needs air-defence systems "in order for rockets not to kill children in their strollers," she said.

"Help us to stop this terror against Ukrainians," she said.

She invoked both the memory of the Sept 11 terrorist attacks and the US Declaration of Independence's call for all people to enjoy "life, liberty and the pursuit of happiness."

US lawmakers will go on recess next week and "this is normal," she said.

"It is precisely this normalcy that we are deprived of now. Will my son be able to return to school in the fall? I don't know, like millions of mothers in Ukraine."

Both President Joe Biden, whom she met on Tuesday, and the US Congress have been enthusiastic about supplying weapons to Ukraine, approving a US$40 billion (S$55 billion) package in May.

But with Russian forces advancing in the east, Ukraine has been seeking to secure a more steady flow of weapons including longer-range precision rockets.

US lawmakers applauded Zelenska as she thanked them for assistance and said, "While Russia kills, America saves."