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The package includes 6,000 missiles, anti-tank and high explosive weapons, and £25 million ($33m) in financial backing for the Ukrainian military.
This more than doubles the defensive aid already provided to more than 10,000 missiles and comes on top of the £400m the UK has committed in humanitarian and economic aid to Kyiv.
Mr Johnson will set out the UK’s intention to work with partners in strengthening Ukraine’s defences, including longer-range targeting and intelligence, as the Ukrainian people battle Russia's invasion.
The UK will also provide an additional £4.1m for the BBC World Service as part of a cross-government effort to tackle disinformation in Russia and Ukraine, and new financial and policing support for the International Criminal Court’s investigation into reported war crimes.
Mr Johnson will welcome Nato and the G7’s unified stance on Ukraine and collective action on economic, military and diplomatic measures.
He will urge allies to increase their response to Russia’s use of increasingly brutal tactics through better defensive support for Ukraine and increasing economic sanctions against the Kremlin.
“[Russian President] Vladimir Putin is already failing in Ukraine,” Mr Johnson said.
“The Ukrainian people have shown themselves to be extraordinarily brave and tenacious in defending their homeland in the face of an unprovoked onslaught.
“But we cannot and will not stand by while Russia grinds Ukraine’s towns and cities into dust.
"The United Kingdom will work with our allies to step up military and economic support to Ukraine, strengthening their defences as they turn the tide in this fight.
“One month into this crisis, the international community faces a choice. We can keep the flame of freedom alive in Ukraine, or risk it being snuffed out across Europe and the world.”
The UK has already provided more than 4,000 anti-tank weapons to Ukraine’s armed forces, including Next-Generation Light Anti-Tank Weapons Systems and Javelin missiles.
The government is also supplying Starstreak high-velocity missiles to help Ukrainians defend themselves against aerial bombings, and body armour, helmets and combat boots.
The £25m in new funding from the Foreign, Commonwealth and Development Office's Conflict Security and Stabilisation Fund will help to pay the salaries of Ukrainian soldiers, pilots and police, and ensure the armed forces have access to high-quality equipment.
The funding for the BBC World Service has been provided by the Department for Digital, Culture, Media and Sport and the Foreign Office.
In addition to the £400m, complemented by donations from the British public, the government has also sent more than four million items of medical equipment and 500 mobile generators.
Justice Secretary Dominic Raab will lead a meeting of justice and foreign ministers in The Hague to co-ordinate support for the International Criminal Court’s war crimes investigations.
Mr Raab, also the Deputy Prime Minister, is expected to announce another £1m in funding for the court, and new support from UK soldiers with expertise in intelligence gathering and the Met Police’s War Crimes Team.