There are an estimated 20,000 warheads in the world's combined stockpile of nuclear weapons.

Of these, almost 5,000 are considered operational and about 2,000 belonging to the US and Russia are believed to be ready for use at short notice.

Although the exact number of nuclear weapons in each country's possession is top secret, the Federation of American Scientists has made best estimates about the size and composition of national nuclear weapon stockpiles based on publicly available information.

Their sources include the Bulletin of the Atomic Scientists and the Stockholm International Peace Research Institute .

*Strategic weapons are designed to target cities, missile locations and military headquarters as part of a strategic plan

**Total arsenal inventory includes non-strategic and non-deployed weapons as well as stockpiles