Siegfried Hecker, a Stanford University Professor and former head of the Los Alamos National Laboratory, disclosed that at a closed-door meeting with US nuclear specialists that he had attended, Chinese officials had conveyed that as per their estimates North Korea may ­already have 20 warheads, as well as the capability of producing enough weapons-grade uranium to double its arsenal by next year. US Admiral William Gortney, head of US Northern Command, earlier this month said that defence officials believed North Korea could now mount a nuclear warhead on an intercontinental ballistic missile called the KN-08. Experts estimate that, thought it may not have been tested yet, the KN-08 has a range of about 9000 kms.