India, Oct. 8 -- MINNEAPOLIS - Federal prosecutors and law enforcement officials in Minnesota announced a significant counterterrorism operation resulting in the arrest of an 18-year-old Twin Cities resident who allegedly planned a mass-casualty terrorist attack at the Mall of America.

The suspect, identified in federal court documents as Sheikhdoon Abdullahi Mohamud, was taken into custody after a sting operation orchestrated by the Federal Bureau of Investigation.

According to unsealed criminal indictments, Mohamud had spent months communicating with confidential sources and expressing explicit allegiance to ISIS while orchestrating plans to target civilian crowds at the nation's largest retail and entertainment complex.

The swift in...