A newly signed agreement between Tokyo and Washington allowing Japanese officials access to U.S. military bases in Japan to conduct environmental surveys has flaws, experts said, questioning its effectiveness due to vague wording in the bilateral documents.

The accord, signed between Foreign Minister Fumio Kishida and U.S. Defense Secretary Ash Carter on Monday in Washington, supplements the existing Japan-U.S. Status of Forces Agreement governing the use of U.S. bases in Japan.

Hiromori Maedomari, a professor at Okinawa International University who has authored a number of books on the SOFA, said Tuesday the accord was only half a step forward.