A sudden feud, an impasse or a first step toward a cease-fire are all possible at the summit in Alaska as the two leaders navigate thorny issues such as Ukraine’s territory and NATO expansion.

Mixed feelings in Moscow before Friday’s summit as analysts are sceptical that peace in Ukraine will be secured.

"This is a very difficult issue, and it's one that will require difficult solutions," former US Marine Corps intelligence officer and ex-UN weapons inspector Scott Ritter said