A top officer of the U.S. Navy reaffirmed Washington's commitment to defending a group of Japan-administered islets in the East China Sea under a bilateral security treaty, while taking the rare step of naming China as a potential aggressor.

"We will clearly defend them if they are attacked by China," Adm. Harry Harris, commander of U.S. Pacific Command, said Wednesday at a Washington think tank event, referring to the Senkakus, a group of islets also claimed by China.

U.S. leaders including President Barack Obama have already stated that the 1960 security treaty, which obliges the U.S. military to defend Japan if it is attacked, covers the Senkakus, but have not specified a potential aggressor.