The United States may deploy further strategic assets to South Korea in the wake of the latest nuclear test by the North.

Washington and Seoul are in talks towards sending further strategic US assets to the Korean peninsula, a day after a US B-52 bomber flew over South Korea.

"The United States and South Korea are continuously and closely having discussions on additional deployment of strategic assets," Kim Min-seok, spokesman at the South Korean Defense Ministry said on Monday, declining to give specifics.

South Korean media said strategic assets Washington may utilize in Korea included B-2 bombers, nuclear-powered submarines and F-22 stealth fighter jets.

Seoul also said on Monday that 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" starting from Tuesday.

North Korea says it exploded a hydrogen bomb last Wednesday, although the United States and other critics doubt this.

In a show of force in the region, the United States on Sunday sent a nuclear-capable B-52 bomber based in Guam on a flight over South Korea.

Separately, South Korea and Japan used their shared military hotline for the first time in the aftermath of North Korea's nuclear test, Seoul's Defense Ministry said, a sign the North's provocation is pushing the two longtime rivals, which are Washington's main allies in the region, closer together.

South Korea has also resumed anti-North propaganda broadcasts using loudspeakers along the border, a tactic that the North considers insulting and resulted in an armed standoff that included an exchange of artillery fire the last time South Korea used the speakers in August.