Ukraine is reportedly prepared to launch British long-range missiles at Russian positions in annexed Crimea, which would signal a significant escalation of western involvement in the conflict.
The announcement comes as Ukrainian forces prepare for the threat of a large-scale offensive from Russian troops over the coming days.
A Ukrainian military official has warned that Putin's forces have amassed 1,800 tanks, 3,950 armoured vehicles, 2,700 artillery systems, 810 Soviet-era multiple-rocket-launch systems, 400 fighter jets and 300 helicopters in preparation for "a new wave of attacks", according to Foreign Policy.
It is believed that discussions are taking place within Downing Street over providing the Ukrainian forces with Harpoon anti-ship missiles or surface-to-air Storm Shadows.
Ukrainian defence sources told The Times that their forces would be prepared to strike Crimea, which has been under Russian occupation since 2014.
President Zelensky has vowed that longer-range weapons provided by western allies would strike “deep in the occupied territories”.
Addressing journalists at a joint press conference with Rishi Sunak, Mr Zelensky said: "You've just asked me what would happen if we don't get these fighter jets or longer-range missiles, or we don't have enough ammunition, because everything obviously is running out and coming out of maintenance.
"Without the weapons that we are discussing now and the weapons that we just discussed with Rishi earlier today and how Britain is going to help us, you know, all of this is very important.
"Without this, there would be stagnation which will not bring to anything good."
The Ukrainian leader said that long-range missiles would help his forces "make the evil completely retreat from our country by destroying its airbases deep in the occupied territories".
He has also voiced frustration with Germany over its commitment to providing weapons, saying he is "constantly having to convince" Chancellor Olaf Scholz to help equip Ukraine in its fight against Russia.
Mr Zelensky said in an interview with German news website Spiegel: "I have to exert pressure to help Ukraine and constantly convince him that this help is not for us but for Europeans. Our relationship to Germany goes in waves, it is up and down."
As the UK government deliberates on whether or not to provide British fighter jets to the Ukrainian military, Downing Street has reiterated its commitment to training the country's pilots “as quickly as humanly possible”.
Rishi Sunak, who promised further support for Ukraine during the British leg of Mr Zelensky’s visit, said the offer of pilot training was the “first step” which could lead to the eventual supply of fighter planes.
“We’re talking about further support, potentially with aircraft as well,” the Prime Minister said.
“The important first step of that journey is to make sure that we provide the training for Ukrainian pilots to be able to use that very sophisticated equipment.”
The UK is “exploring how quickly this can be done,” No 10 said in a briefing.
