South Korea is losing patience with the North and probably will take military action, former US national intelligence director Dennis Blair has said.
Mr Blair, who recently returned from the Korean peninsula, said he does not see a major war starting, but he believes recent aggression by the North will press South Korea into some lower-level military confrontations.
He said there was support among South Koreans for their military to take a stronger stance, adding that "a South Korean government who does not react would not be able to survive there".
He told CNN's State of the Union that the North's recent moves to sink a South Korean ship and fire artillery rounds on a South Korean island near a disputed sea border have frayed Seoul's patience.
The artillery attack killed four South Koreans, while 46 sailors died in the sinking of the ship.
Mr Blair said that what is needed is a united Korea under Seoul's influence, but China would have to exert its influence on the North for that to happen, and Beijing prefers the two countries to remain divided.