Efforts to secure the full implementation of a ceasefire in Ukraine are set to dominate a gathering of world leaders in Italy.
David Cameron is among representatives of more than 50 nations in Milan, Italy for the Asia-Europe Meeting (ASEM), including Chinese premier Li Keqiang.
The Prime Minister hopes to use the summit to push for greater international action to deal with the Ebola virus outbreak.
But talks between Russian president Vladimir Putin and his Ukrainian counterpart Petro Poroshenko on the margins of the event are drawing the greatest attention.
The talks are the first between Mr Putin and EU leaders about the crisis since June - at D-Day anniversary commemorations in France - and come at the time of the worst relations between Moscow and the West since the end of the Cold War.
Mr Cameron, French president Francois Hollande, German chancellor Angela Merkel and Italian prime minister Matteo Renzi are due to be involved in the discussions.
On Wednesday, they - along with US President Barack Obama - called on Moscow to do more to respect a ceasefire, stop the flow of weapons across the border, ensure free and fair elections and and an energy dispute which had sparked fears for supplies of gas to the EU.
A series of economic sanctions have been imposed by the EU and Washington to punish Mr Putin's regime for its annexation of Crimea and support for the separatists, who Moscow denies arming.
At the weekend Mr Putin pulled back 17,600 Russian troops from the border region with Ukraine in an apparent show of goodwill ahead of a diplomatic push.
Mrs Merkel told reporters she was expecting "an open exchange of views and progress in implementing the Minsk Agreement" when she meets face-to-face with the Russian president.
The United Nations has reported at least 331 deaths in eastern Ukraine since last month's ceasefire between Russian-backed separatists and government troops, with the main rebel-held city of Donetsk still the scene of clashes.
Some 3,660 are thought to have been killed in the six months since fighting began.