Firearms are the leading cause of death for US young people aged 18 to 25, surpassing drug poisoning and other causes.
The expert-level technical talks could determine the specifics of nuclear and sanctions commitments by the two sides.
Dozens of heads of state - some of whom had better relations with the pope than others - will be in attendance.
Kremlin aide says discussion focused on the 'possibility' of resuming direct negotiations between Russia and Ukraine.