A published report says the United States and Japan will declare for the first time in a joint agreement that Taiwan is a mutual security concern.

The Washington Post newspaper, citing a draft copy of the document, says the agreement will be announced after a meeting in Washington Saturday between Secretary of State Condoleezza Rice, Defense Secretary Donald Rumsfeld and their Japanese counterparts.

The Post calls the move the most significant alteration since 1996 to the U.S.-Japan Security Alliance. It follows an assessment earlier this week by CIA director Porter Goss that China's military buildup is tilting the balance of power in the Taiwan Strait.

Beijing considers Taiwan a renegade province and has threatened to attack the island if it moves toward independence.