SHIJIAZHUANG, Sept. 23 (Xinhua) -- Four Japanese are being investigated in China for having entered a military zone without authorization and illegally videotaped military targets in northern Hebei Province, local state security authorities said Thursday.

The state security authorities in Shijiazhuang, capital of Hebei, have taken measures against the four people according to law after receiving a report about their illegal activities.

The authorities only gave one name of the four Japanese nationals, Sada Takahashi.

"Currently, the case is being investigated," the state security authorities in Shijiazhuang said in a statement.

No further details were provided.