China has detained four Japanese employees of construction company Fujita Corp., reportedly for entering a military zone in Hebei Province without authorization and videotaping military targets, Chief Cabinet Secretary Yoshito Sengoku said Friday.

Partially confirming Sengoku's remarks, Tokyo-based Fujita said Friday it hasn't been able to contact five of its workers in China, including four Japanese nationals, since Monday.

"We are very sorry to make the public worried," Tatsuro Tsuchiya, Fujita's senior operating officer, told a news conference. "We pray for an early resolution to this matter."