The West must give Ukrainian armed forces "advanced, Nato-standard capabilities", including longer-range weapons, the Prime Minister has said at the Munich Security Conference in Germany.
Rishi Sunak reiterated the UK's resolve in supporting Ukraine, saying that the UK became the first country to provide Ukraine with tanks, as well as being the first to offer training to Ukrainian pilots and marines.
The Prime Minister said: "Together we must help Ukraine to shield its cities from Russian bombs and Iranian drones, that's why the United Kingdom will be the first country to give Ukraine longer-range weapons."
The move comes after Ukraine said it would use British long-range missiles – if they were supplied by the UK – to hit Russian forces inside Crimea.
According to defence experts, British missiles such as Storm Shadow would provide the Ukrainian forces with the ability to hit Russian targets that are currently out of reach.
To repel Russian aggression Rishi Sunak said that western leaders must band together and "double down" on military support for the war-torn country.
The Prime Minister stated that the only way to stop the pain and suffering inflicted by Russian forces is "for Ukraine to win".
"To win the war, Ukraine needs more artillery, armoured vehicles and air defence," Sunak said.
The UK will also be extending its training mission – which has already seen 10,000 Ukrainian troops come to the UK – to cover fighter jet pilots, ensuring Ukraine can defend its skies using "Nato tactics" in the future.
The training of pilots is expected to commence in the spring, according to Downing Street officials.
The Prime Minister's visit to Germany comes as some in Ukraine suggest a spring-time offensive by Russian president Vladimir Putin's forces has already begun along parts of the eastern frontline.
Mr Sunak told the forum that the West, in the face of ramped-up Russian attacks, must continue to back Kyiv.
"When Putin started this war, he gambled that our resolve would falter. Even now he is betting we will lose our nerve.
"But we proved him wrong then, and we will prove him wrong now."
In an apparent attempt to encourage others in the West to offer long-term training to Kyiv's armed forces, the Conservative Party leader warned leaders that Ukrainians are fighting for the security of all nations.
"We need to do more to bolster Ukraine's long-term security," Mr Sunak said in his speech.
"We must give them the advanced, Nato-standard capabilities that they need for the future.
"And we must demonstrate that we'll remain by their side, willing and able to help them defend their country again and again.
"What's at stake in this war is even greater than the security and sovereignty of one nation.
"It’s about the security and sovereignty of every nation.
"Because Russia's invasion, its abhorrent war crimes and irresponsible nuclear rhetoric are symptomatic of a broader threat to everything we believe in."
In the last year, No 10 officials said £2.3bn of UK military support to Ukraine has provided a squadron of Challenger 2 tanks, 200 other armoured vehicles and more than 10,000 anti-tank missiles and multiple-launch rocket systems.
The Prime Minister has said he is committed to matching or exceeding that level of support this year.
Sir Keir Starmer, who has been visiting Ukraine in recent days, said a Labour administration would maintain the defence, training and technical support the Government is providing.
"Throughout this conflict, I've made clear that there will be no difference between the UK political parties on this," the Labour leader said.
"We will continue to work with the Government to see what further support we can provide, but any support must be provided in lockstep with Nato powers."
Sir Keir added that "there must also be justice, and reparations for the rebuilding of Ukraine".
Addressing the forum in Munich, United States Vice President Kamala Harris said that Russia must be held accountable for "crimes against humanity" and that Nato's resolve was stronger than ever.