Russia and the United States together hold about 90 percent of the world ' s nuclear weapons while keeping them “unnecessarily excessive” at high alert, a report says.

As of early 2013 Russia ' s total nuclear inventory is about 8,500, slightly surpassing that of 7,700 in the US, a report by the Bulletin of the Atomic Scientists published in the United States says.

According to the Bulletin, Russia and the United States keep a staggering 1,800 strategic nuclear warheads on high alert on land - and sea - based ballistic missiles, ready to launch between 5 and 15 minutes after receiving a launch order.

The Bulletin of the Atomic Scientists estimates the total number of nuclear warheads in the world to be 17,300. France is the third biggest nuclear power with 300 warheads, followed by China with 250 and the United Kingdom with 225.

The practice of keeping nuclear weapons on alert evolved during the Cold War, as the United States and the Soviet Union deployed fully - armed nuclear weapons that could strike the adversary before it could retaliate.

France and Britain also deploy 80 and 48 fully operational nuclear weapons, respectively, but on their missile submarines, and also at a lower readiness level than Russia and the United States forces.

Other nuclear weapon states do not see a need to keep nuclear forces on alert, despite their much smaller arsenals.

the report says " Even if one believes that some nuclear alert is necessary, the number of weapons that Russia and the United States keep on alert seems far too large at a time when much else from the Cold War has faded, and Russian - US goods trade reached nearly $43 billion in 2011 ".

The high level of nuclear alert locks the countries’ nuclear planning into unnecessarily excessive and expensive threat postures that are out of sync with the political and military realities of today’s world, the report says.