South Korea is "aware" of fresh signs that North Korea may be preparing for a second nuclear weapon test and has strengthened its intelligence-sharing with the United States, Yonhap News quoted a government official as saying Tuesday.

The unidentified official, in the wake of media reports U.S. spy satellites have detected suspicious activity at North Korean sites that could be preparations for another test, said, "We are preparing for uncertainties but are very cautious in analyzing North Korea- related intelligence."

He said the detected activity could be simply part of military activities unrelated to a nuclear bomb test.

South Korea and the United States have confirmed that North Korea conducted an underground nuclear explosion on Oct. 9.

Christopher Hill, Washington's point man on Pyongyang, is due to arrive in Seoul on Tuesday to lay the groundwork for a trip here by U.S. Secretary of State Condoleezza Rice, who will meet Thursday with Foreign Minister Ban Ki Moon, Yonhap reported.

Rice's upcoming visits to Japan, South Korea, China and Russia are aimed at following up on the resolution passed last weekend by the U.N. Security Council that calls for wide-ranging arms and financial sanctions against North Korea.