SEOUL, South Korea - The Pentagon's chief says the threat of nuclear missile attack by North Korea is accelerating.

  

And U.S. Defense Secretary Jim Mattis - during a visit to South Korea - is accusing the North of illegal and unnecessary missile and nuclear programs, and pledging to repel any strike.

  

Mattis says North Korea engages in in what he calls "outlaw" behavior and he says the U.S. will never accept a nuclear North.

  

Mattis says regardless of what the North might try, it is overmatched by the firepower and cohesiveness of the decades-old U.S.-South Korean alliance.