Britain will supply Ukraine with more multiple-launch rocket systems that can strike targets up to 80 km (50 miles) away.
Defence Secretary Ben Wallace said the supply of weapons would help Ukraine defend itself against Russian heavy artillery.
"This latest tranche of military support will enable the Armed Forces of Ukraine to continue to defend against Russian aggression and the indiscriminate use of long-range artillery," Wallace said in a statement.
"Our continued support sends a very clear message, Britain and the international community remain opposed to this illegal war and will stand shoulder-to-shoulder, providing defensive military aid to Ukraine to help them defend against Putin's invasion." (Reporting by Sachin Ravikumar and Andrew MacAskill; Editing by Kate Holton)