U.S. Defense Secretary Robert Gates has expressed serious concerns over the possibility of a group like al-Qaida obtaining a weapon of mass destruction from North Korea.

In an interview with U.S. broadcaster CBS on Monday, Gates said fears persist that terrorist groups, like the one headed by Osama bin Laden, could get weapons of mass destruction from countries such as Pakistan or North Korea.

Gates also said he is seriously disappointed with the amount of troops deployed to Afghanistan from NATO member countries, excluding the United States.