"The United States and South Korea are continuously and closely having discussions on additional deployment of strategic assets," Kim Min-seok, a South Korean defense ministry spokesman, said, Reuters wrote.
South Korean media said the United States may send to South Korea B-2 bombers, nuclear-powered submarines and F-22 stealth fighter jets.
South Korea also said it would restrict access to the jointly run Kaesong industrial complex just north of the heavily militarized inter-Korean border to the "minimum necessary level" from Tuesday.
As reported earlier, North Korea said it set off a hydrogen bomb last Wednesday, its fourth nuclear test since 2006, angering China, the North's main ally, and the United States, which said it doubted the device was a hydrogen bomb.
