The British government has accused Russia of targeting populated areas "in multiple locations", noting in an intelligence update. that it had "previously used similar tactics in Chechnya in 1999 and Syria in 2016".
On Sunday, UN monitors said 364 civilian deaths had been confirmed in Ukraine since the invasion began on 24 February, but the real figure was likely to be "considerably higher".
The UNHCR said more than 1.5 million people had fled Ukraine since Russia invaded.
But Russia denies targeting civilians, saying it is carrying out a "special military operation" against Ukrainian "nationalists" and "neo-Nazis".
Ms Stefanishyna - who was speaking to BBC TV's Sunday Morning programme - accused Russia of "military tactics right in the cities of Ukraine", adding they were carrying out a "terroristic plan", with attacks coming from the air and also by land.
"Shelled hospitals, the shelled houses for kindergartens and schools, and the ordinary households," she said. "This is how the reality looks."
She said Ukraine was seeing "another wave of implementation of this terroristic plan of [the] Russian Federation".
Ms Stefanishyna claimed Russia was suffering "enormous losses" of soldiers and equipment, but this "does not deter Russia".
"It only encourages further aggression," she said.