PTI, Washington : The US has pressed Pakistan to reduce its growing nuclear arsenal but Islamabad has refused to accept any curbs on it saying America must show “greater understanding” of its security concerns in South Asia.Citing the example of the US and Russia which are working to further reduce their nuclear arsenals, Secretary of State John Kerry asked Pakistan to understand this reality and review its nuclear policy.The nuclear issue was discussed during security talks held in Washington yesterday as part of the US-Pakistan strategic dialogue.”I think, it is important for Pakistan to really process that reality and put that front and centre in its policy,” Mr Kerry said in an apparent reference to the reports that Pakistan has the fastest growing stockpile of nuclear weapons in the world.His remarks come ahead of this month’s Nuclear Security Summit to be hosted by President Barack Obama that would be attended by Pakistan Prime Minister Nawaz Sharif.”We look forward to Prime Minister Nawaz Sharif’s participation in the nuclear security summit next month,” Mr Kerry said, adding “non-proliferation” and “nuclear safety” is of obvious concern to both countries.”I expect that we continue to discuss the obligation of being a responsible state with nuclear weapons in the coming year,” he said.”As you know United States of America once had 50,000 (nuclear) warheads pointing at another country/entity the Soviet Union. Soviet Union had 50,000 pointing at us. It took two Presidents (Mikhail) Gorbachev and (Ronald) Reagan to decide that this did not make sense,” Mr Kerry said.Meanwhile, identifying the “strategic and conventional imbalance with India” as the topmost security threat to it, Pakistan today rejected America’s call to reduce or cap its nuclear weapons arsenal, believed to be the fastest growing in the world.”I think (Pakistan’s top) security concern is strategic and conventional imbalance with India,” the Pakistan Prime Minister’s Advisor on Foreign Affairs Sartaj Aziz told Defence Writers Group in a breakfast meeting this morning.