Russia and the US are two leading nuclear powers, the nature of their interaction largely determines stability and global security, Leonid Slutsky, chairman of the State Duma Committee on International Affairs and leader of the LDPR, said

"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

Putin has met with American presidents many times over the decades - some more often than others.