The United States has denied some media speculation that a large explosion in North Korea last week might be related to the communist country's suspected nuclear weapons program.

Speaking on ABC's "This Week" Sunday, Secretary of State Colin Powell said there was no indication that the recently reported explosion in North Korea was a nuclear event of any kind, adding that it was not yet known what caused it.

Powell said there were some activities taking place and some sites that Washington is watching carefully, adding it was not conclusive that the communist state was moving toward a nuclear test.

According to Seoul-based Yonhap News Agency, the explosion occurred on Thursday in Yanggang province near the border with China.

Meanwhile, U.S. National Security Adviser Condoleezza Rice said on CNN's "Late Edition" on Sunday that Washington doesn't think, at this point, that the explosion was a nuclear event. However, she was quick to add that Washington is still looking at the blast and will make further analysis.

In Seoul earlier on Sunday, presidential spokesman Kim Jong-min said South Korea does not think North Korea conducted a nuclear test, and they are trying to find out in detail the exact character, cause and size of the blast.