The global arsenal of nuclear warheads stands currently at 16,300, a drop of just under 1,000 from 2013, a Sweden-based peace research institute reported on Monday.

Israel's arsenal stands at 80 warheads, the institute said, the same number it reported in 2013.

The number of operational weapons at present is approximately 4,000, according to the annual data released by the Stockholm International Peace Research Institute. But the number jumps to 16,300 when warheads that are in storage or ready to be dismantled are included.

The global nuclear arsenal is dominated by the two nuclear heavyweights - the United States and Russia – which jointly have just over 90 per cent of the world's nuclear arsenal. The US has an estimated 7,300 warheads, while Russia 8,000.

Altogether, nine states are believed to possess nuclear weapons: the U.S., Russia, Britain, France, China, India, Pakistan, Israel and North Korea.

The SIPRI researchers said nuclear powers continued to upgrade their nuclear forces and delivery systems during the past year.

The US has allocated $350 billion to upgrading and maintaining its nuclear forces in the coming 10-year period, including investing in new submarines and reviewing new ballistic missiles and long-range bombers, the think tank said.

Russia, in addition to upgrading its ballistic missiles, was reportedly developing a new type of submarine to be able to launch nuclear weapons at sea.

India and Pakistan continued to develop ballistic and cruise missiles and also to produce fissile material for military purposes.

India was estimated to have about 90 to 110 nuclear warheads, Pakistan between 100 and 120, while Israel's stock remained at 80, according to SIPRI.

China's arsenal numbered 250 warheads, of which 190 were designated for its land-based ballistic missiles and aircraft.

North Korea, which conducted its first nuclear test in 2006, was believed to have 6 to 8 nuclear weapons, SIPRI said.