World leaders will begin arriving in the UK today ahead of the start of a two-day Nato summit in Wales tomorrow.
Some 61 heads of state are expected to gather at The Celtic Manor Resort outside Newport, with the ongoing conflict in Ukraine set to top the agenda of discussions.
Leaders will be joined by officials from the European Union, the UN, the International Monetary Fund and the World Bank.
A further 5,000 delegates are expected to gather to discuss the future of the Nato alliance.
Speaking at Downing Street ahead of the summit, David Cameron has condemned the ongoing violence in Ukraine, describing it as “disgraceful”.
He told an audience of international delegates in London on Tuesday night: “What’s happening in the Ukraine right now is disgraceful and completely unacceptable.
“Members of Nato want and deserve real reassurance that our Article V commitments are rock solid.”
He said he wanted the upcoming conference to demonstrate a “very clear, unified and strong message” about the importance of Nato globally.
Foreign Secretary Philip Hammond has also warned that Nato must show it still has the political will to fight back in the event of a Russian attack on any member states.
Western nations have repeatedly accused Russia of intervening militarily in the conflict in Ukraine. The claims have been denied by Moscow.
Mr Hammond said: “For Nato to maintain its credibility in the future, we have to demonstrate that we maintain the political will to act to defend ourselves and our interests.
“We have to be clear that we have not lost the appetite to intervene when our interests or our obligations require us to do so.
“If we lack, or are perceived to lack, the political will to respond – and to do so quickly – the credibility of that commitment to collective defence will be undermined, and the very fabric of this, most successful of alliances, will unravel.
“So we have to be clear with Russia, in particular, that while we support a political resolution to the situation in eastern Ukraine, there is a red line around Nato member states themselves that cannot be crossed.”
Nato’s Secretary General Anders Fogh Rasmussen says the alliance is set to create a high-readiness force in Eastern Europe as a bulwark against potential Russian aggression.
Mr Rasmussen said the unit would be a spearhead that could be deployed at very short notice to help Nato members defend themselves against any threat.
The murder of another US journalist by Islamic State militants will also feature in bilateral discussions between Western allies at the summit.
US President Barack Obama will head to Wales after a visit to the Baltic States.