The South Korean government said there was no evidence supporting reports from Washington that North Korea appeared to be preparing for an underground nuclear test.
"Although (North Korea testing a nuclear weapon) is logically possible, no activity has been detected," a South Korean official said on condition of anonymity.
The official added the government was "closely sharing intelligence information with Washington."
Saying that it was always difficult to verify a nuclear-related activity, the official cited a previous case in 1998 when Washington claimed North Korea could be preparing for a nuclear test in Geumchang-ri. The claim later turned out to be a false alarm.
South Korea believes that North Korea is now technically capable of carrying out a nuclear test.