another weapons expert told cnn they were likely just mock ups but it could hit targets in the mainland u.s. and europe. cnn's brian todd has the very latest assessments of where north korea's technology stands. >> reporter: kim jung-un's nuclear build up is advancing rapidly. north korea having produced 13 and 30 nuclear warheads according to a new report from david albright whose team examined the production. north korea's nuclear program is so secretly that completely accurate figures are difficult to get. based on what he found, he has an ominous projection for the number of warheads kim could soon produce. >> by the end of 2020, the numbers could go up to 25 to 50 and the worst case could go up to 60. >> reporter: with a stockpile that large, analysts say, kim's