Police officers stand guard at the Universal City subway station in Los Angeles, the United States, Dec. 6, 2016. FBI, Los Angeles Police Department (LAPD) and sheriff's department officials said they received a telephone call about an imminent but uncorroborated threat against the Metro Red Line in Universal City on Monday. The threat came from overseas through an anonymous phone call to a public safety line. (Xinhua/Zhao Hanrong)