The prime minister said the UK will send additional military equipment including Starstreak anti-aircraft missiles and 800 anti-tank missiles.
It comes after dozens of people died when a crowded railway station in eastern Ukraine was hit by rockets.
Vladimir Putin’s daughters have also been sanctioned by the UK.
Speaking at a Downing Street press conference with German Chancellor Olaf Scholz, Mr Johnson warned Russia will not escape punishment after the attack at Kramatorsk station.
He said: “I know that Britain and Germany share exactly the same sense of horror and revulsion at the brutality unleashed including the unconscionable bombing of refugees fleeing their homes this morning.
“It is a war crime indiscriminately to attack civilians, and Russia’s war crimes in Ukraine will not go unnoticed or unpunished.”