Members of the mostly European 'coalition of the willing' discussed security cooperation for Ukraine on Tuesday, and top NATO generals were also to broach the topic on Wednesday. Key issues include the role of the US and a possible mutual assistance clause.

Ukraine and its European allies have been buoyed by Trump's promise during a summit on Monday of security guarantees for Kyiv, but many questions remain unanswered. Officials told Reuters that the Pentagon is carrying out planning exercises on the support Washington could offer beyond providing weapons.