It noted success in turning the plutonium it had extracted into weapons-grade material . January : North Korea blocks South Korean workers from jointly run industrial facilities . The North is ` ` fully prepared '' to defend itself , Kerry says . U.N. Secretary - General Ban Ki - moon ` ` deeply troubled '' about North Korea 's statements . The North says it is rebuilding and restarting operations at its main nuclear complex .
January : North Korea blocks South Korean workers from jointly run industrial facilities . The North is ` ` fully prepared '' to defend itself , Kerry says . U.N. Secretary - General Ban Ki - moon ` ` deeply troubled '' about North Korea 's statements . The North says it is rebuilding and restarting operations at its main nuclear complex .