U.S. Secretary of Defense Robert Gates says that with North Korean leader Kim Jong-il reportedly in poor health, the power succession process may be driving the nation’s increasingly provocative behavior.

Gates made the remarks in a lecture hosted by the Marines' Memorial Association in San Francisco on Thursday.

Gates also suggested that the sinking of South Korea’s “Cheonan” naval vessel may have been done in order to establish military credibility for the North Korean leader’s third son and heir apparent, Jong-un.

Gates said that he is concerned that this may not be the only provocation from the North Koreans.

The defense secretary added that China is reluctant to pressure North Korea into abandoning its nuclear programs and provocations because Beijing is worried that a collapse of the North Korean government would send millions of refugees into China.

Gates said that North Korea poses a serious threat to the security of the U.S. by developing long-range missiles and nuclear weapons, adding that the communist country has been continuously attempting to export missiles and weapons to Myanmar, Iran, Hezbollah and Hamas.