NEW YORK, Dec. 31 (UPI) -- The United Nations secretary general says he will work with the four nations U.S. President Bush says are coordinating responses to South Asia's tsunamis.

Some officials, concerned about duplication and confusion, have criticized the United States, India, Australia and Japan for forming an ad hoc core group of nations to coordinate worldwide relief and reconstruction.

Monster waves produced by Sunday's earthquake beneath the Indian Ocean have killed an estimated 124,000, injured about a half million more and left millions with little or no access to food or clean water.

U.N. Secretary General Kofi Annan said he saw no conflict between the United Nations and the core group.

"Above all, I would like to assure the people of the region that the entire United Nations family stands ready to assist, and we stand behind them," he declared. "We will work with them in every way we can to rebuild their lives, livelihoods and communities devastated by this catastrophe."