European leaders vowed on Thursday to strengthen Kyiv's army to ensure it was the cornerstone of future security in Ukraine, while France and Britain tried to expand support for a planned foreign "reassurance force" in the event of a truce with Russia.

It was the third summit of what Britain and France have called the "coalition of the willing," reflecting concern among Europeans that the U.S. no longer represents a bulwark of support for Ukraine's 3-year-old fight against Russian invasion.

Progress on what role Europe might play in providing peacetime security guarantees is proving difficult with the prospect of a ceasefire distant and much dependent on how Russia responds and to what extent the U.S. would support its allies.