"The president indicated he would continue to consult our allies and partners in the days ahead to ensure provocative actions from North Korea are met with serious consequences," White House press secretary Josh Earnest said.
He said President Obama was briefed on the situation as he flew home from a visit to Asia aboard Air Force One.
Obama consulted with South Korean President Park Geun-hye and Japan's Prime Minister Shinzo Abe in separate phone calls from the presidential aircraft.
Earlier, National Security Council spokesman Ned Price said the US was monitoring and continuing to assess the situation in view of the seismic activity on the Korean Peninsula in the vicinity of a known nuclear site.
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"We are monitoring and continuing to assess the situation in close coordination with our regional partners," Price said.
His statement came after South Korean and international monitoring agencies reported an earthquake near North Korea's north-eastern nuclear test site, indicating that Pyongyang may have detonated a new atomic test to mark the 68th anniversary of the country's founding.
"The event seems to have been slightly larger than the one our system recorded on 6 January this year and the location is very similar to that event. Our initial location estimate shows that the event took place in the area of the DPRK's nuclear test site.
"If confirmed as a nuclear test, this act constitutes yet another breach of the universally accepted norm against nuclear testing; a norm that has been respected by 183 countries since 1996," she said.