NEW DELHI: India and Pakistan have added 20-30 nuclear warheads in their arsenal in the past one year, a global think tank said on Tuesday.In its latest yearbook, Stockholm International Peace Research Institute said the neighbours are continuing to develop new ballistic and cruise missile systems capable of delivering nuclear weapons.In 2010, the Indian nuclear arsenal had 60-80 nukes but they have increased to 80-110 warheads. On the same pattern, the Pakistani side also increased its warheads from 70-90 to 90-110 warheads in the same period, SIPRI said in a release."India and Pakistan continue to develop new ballistic and cruise missile systems capable of delivering nuclear weapons. They are also expanding their capacities to produce fissile material for military purposes," it said.India, Pakistan and six other countries -- the US, the UK, Russia, France, China and Israel -- possess more than 20,500 nuclear weapons, a drop of more than 2000 since 2009.More than 5000 of these weapons are deployed and ready for use, including nearly 2000 that are kept in a state of high operational alert.India carried out its first nuclear test in 1974 in Pokhran and followed up again in 1998 at the same place. Soon after the 1998 tests, India declared a 'no-first use' policy of nuclear weapons and has been developing a credible nuclear response capability in view of it.It has already developed a triad of nuclear delivery systems with the development of land, sea and air-based weapon systems.