N.Korea could have 20 nuclear bombs by 2016: US expert

North Korea could possess some 20 nuclear bombs by 2016, according to a prominent U.S. nuclear scientist.

Siegfried Hecker, a research professor at Stanford University, made the prediction on Thursday, when he met with a group of South Korean lawmakers at the National Assembly.

Hecker, who once visited secretive North Korea's Yongbyon nuclear complex in 2010, said that the North will carry out more detonation tests to miniaturize its nuclear warheads.

Meanwhile, Seoul's defense ministry said on Thursday that it is closely monitoring North Korea's recent move to sharply step up its warfare drills.