The number has come down from a high of more than 70,000 in 1986, as the US and Russia have gradually reduced their massive arsenals built up during the Cold War, the France 24 reported.
But this era of disarmament appears to be coming to an end and the risk of a nuclear escalation is now at its highest point in the post-Cold War period, SIPRI researchers said.
"Soon, we're going to get to the point where, for the first time since the end of the Cold War, the global number of nuclear weapons in the world could start increasing for the first time", Matt Korda, one of the co-authors of the report, told AFP.
After a "marginal" decrease seen last year, "nuclear arsenals are expected to grow over the coming decade", SIPRI said.
Meanwhile several countries, including China and Britain, are either officially or unofficially modernising or ramping up their arsenals, the research institute said.
KI/PR