Ri, in a rare speech to the U.N.-backed Conference on Disarmament, said that joint military exercises being staged by South Korea and the United States were "unprecedentedly provocative in nature and have an especially high possibility of sparking off a war".
"The DPRK (Democratic People's Republic of Korea) cannot but bolster its nuclear deterrent capability to cope with the ever-increasing nuclear threat of the US. Now the DPRK has the power of deterring the US and conducting a pre-emptive strike as well, if necessary," Ri told the Geneva forum.
He said North Korea would spare no effort to bring about "great change in inter-Korean relations this year."