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.