FERGUSON, Mo.—The Federal Bureau of Investigation opened a probe into the shooting death of an unarmed black teenager in this St. Louis suburb, as more unrest broke out late Monday following looting and widespread property damage the previous night.

The FBI will conduct its own investigation in addition to one already under way by St. Louis county police into a shooting by a Ferguson police officer that left 18-year-old Michael Brown dead. The FBI review will focus on whether the civil rights of Mr. Brown were violated.

"Aggressively pursuing investigations such as this is critical for preserving trust between law enforcement and the communities they serve," U.S. Attorney General Eric Holder said in a statement.

Mr. Brown's death touched off protests here, with disorder breaking out for a second night Monday after a vigil late Sunday gave way to looting and property destruction. Police on Monday night fired tear gas into a crowd and barricaded streets leading to Mr. Brown's home. Armored vans shined their spotlights at people on side streets as a helicopter circled the area, sweeping it with an even more powerful spotlight.

A spokesman for the St. Louis County Police said in an interview Monday evening with local television station KSDK that people could protest, but there wouldn't be any looting. Some people threw rocks, bottles and other objects at officers and police made multiple arrests.