Britain said it would donate air defence missiles capable of shooting down cruise missiles to Ukraine in the wake of Russian strikes on Kyiv and other cities in recent days.
British Defence Secretary Ben Wallace announced the new support ahead of a NATO meeting in Brussels on Thursday.
Ukraine's allies had pledged new air defences and more aid on the sidelines of the meeting on Wednesday.
Britain said the Advanced Medium-Range Air-to-Air Missile, or AMRAAM, which will be provided in the coming weeks, could be used with the National Advanced Surface-to-Air Missile System, or NASAMS air defence systems pledged by the United States.
Hundreds of additional air defence missiles of other types would also be donated, along with more aerial drones and a further 18 howitzer artillery guns, it said.
Wallace said: "Russia's latest indiscriminate strikes on civilian areas in Ukraine warrant further support to those seeking to defend their nation.
"So today I have authorised the supply of AMRAAM anti-aircraft missiles to Ukraine."
Many countries have condemned Russia's invasion, which Russian President Vladimir Putin calls a "special military operation" to ensure Russian security and protect Russian-speakers in Ukraine.
Ukraine and its allies accuse Moscow of waging war to grab territory.
U.S. Defense Secretary Lloyd Austin said on Wednesday he expected that Ukraine would do everything it could throughout the winter to regain its territory.
"And we're going to do everything we can to make sure that they have what's required to be effective," he told a news conference in Brussels.
The latest Russian air attacks killed at least 26 people since Monday in Russian missile attacks across Ukraine, wounded more than 100 and knocked out power supplies, adding new urgency to Kyiv's long-standing calls for air defences to protect its cities.
Germany said on Wednesday the first of four IRIS-T air defence systems had reached Ukraine.