Ukrainian President Volodymyr Zelensky will attend a meeting of the 'Coalition of the Willing' in London later today, where leaders are expected to discuss ways to place further pressure on Russia to end its invasion.
Taoiseach Micheál Martin will also join the meeting remotely, as will several other leaders.
The meeting was organised following Mr Zelensky's visit to the White House last week, where he failed to secure US commitments to supply Tomahawk missiles.
It will be hosted by British Prime Minister Keir Starmer and will focus on ways to ramp up pressure on Russia.
Ahead of the coalition meeting, Mr Starmer met with the Ukrainian President.
Mr Starmer said "huge steps forward" had been taken this week to support Ukraine, but there was "further we can do" on long-range capability as he described the UK as Kyiv's "closest supporter and ally".
At the start of the bilateral meeting with Mr Zelensky, the Prime Minister said: "Volodymyr, it's really good to be able to welcome you here in Downing Street again for a really important meeting between the two of us, bilaterally, but also for the coalition of the willing."
He added: "Through seeing His Majesty, through our meeting and through the coalition of the willing, we reaffirm again our support for you and Ukraine and our absolute commitment to meeting the challenge of Russian aggression.
"And whilst you have signalled the path for a way forward and shown that willingness of courage and determination, what we see from Putin is an absolute unwillingness to engage, in fact, the opposite, which is the continued attacks increasingly on civilians and on children and sadly I have to offer you my condolences again, as I did the last time we met and the time before, for those terrible losses.
"I do think that this week we can really bear down on Russian oil and gas. Huge steps forward this week already.
"I think there's further we can do on capability, particularly... long-range capability, and of course, the vital work for coalition of the willing when it comes to the security guarantees that are necessary.
"So we've got really important business to go through with the coalition of the willing today, but it's very good to be able to welcome you back."
Mr Keir said: "We stand, as we've always stood, as your closest supporter and ally."
Earlier, Mr Zelensky met Britain's King Charles at Windsor Castle, where he was given a royal salute and the Ukrainian national anthem was played.
Mr Starmer is expected to announce plans to accelerate the delivery of 140 lightweight multirole missiles to Ukraine.
The delivery is part of a £1.6 billion deal agreed last March between the UK and Ukraine. The multirole missiles are being built in Belfast.
The meeting will also be attended, in person, by NATO Secretary General Mark Rutte and the prime ministers of Denmark and the Netherlands.
Joining the call remotely will be a further 20 leaders.
Mr Martin has already made clear that he is open to Ireland contributing in terms of peace keeping efforts in Ukraine, should a peace agreement be reached.
Meanwhile, EU leaders in Brussels have stopped short of formally endorsing a plan to convert €140 billion in immobilised Russian assets into a long term loan for Ukraine.
It follows opposition from Belgium over the plan's potential legal and financial risks.
Because the bulk of the frozen assets are held in Euroclear, a Belgian-registered depository, the Belgian government sought iron-clad guarantees that it would not be on the hook alone for €140bn if Russia successfully counterclaimed.
All member states except Hungary have said they are anxious to provide those guarantees.
The Belgian prime minister, Bart de Wever, said in the early hours of this morning that he remained to be convinced.
As such, the final text was watered down to say that the EU was committed to supporting Ukraine's financial and military needs for the next two years, while the European Commission was invited to explore options to this end.
European Central Bank President Christine Lagarde told the meeting that the risks involved in converting the Russian assets were manageable.
However, this was not sufficient for Belgium to sign up to stronger language in the final text.
Mr Martin said that Ireland supports the plan, which would ensure Ukraine's financial and military needs are met for the next two years.
Leaders last night said they would revisit the issue at their next summit in December.
The United States has also announced sanctions on Russian oil companies in a bid to pressure Moscow into peace negotiations.
Mr Starmer will call on leaders to "step up" the gifting of "long-range missiles".
Speaking before the meeting he said: "The only person involved in this conflict who does not want to stop the war is President [Vladimir] Putin, and his depraved strikes on young children in a nursery this week make that crystal clear.
"Time and again we offer Putin the chance to end his needless invasion, to stop the killing and recall his troops, but he repeatedly rejects those proposals and any chance of peace."
