Tokyo will "strongly demand" an explanation from Washington about reported allegations that Japanese diplomats in the U.S. were among 38 "targets" of American spying activities, Chief Cabinet Secretary Yoshihide Suga said Monday.

Japan will lodge an inquiry through diplomatic channels with the U.S. about Sunday's report by The Guardian, which quoted what it says is a top-secret U.S. National Security Agency document leaked by fugitive ex-NSA and ex-CIA contractor Edward Snowden.

The Guardian reported that one secret 2010 document lists 38 embassies and missions in New York and Washington that were described as "targets." Among them were those of Japan, as well as Middle Eastern countries, the European Union mission, France, Italy, Greece, Mexico, South Korea, India and Turkey.