A U.S. Army veteran who flew a black Islamic State flag on a truck that he rammed into New Year's revelers in New Orleans shows how the extremist group still retains the ability to inspire violence despite suffering years of losses to a U.

Shamsud-Din Jabbar recently renewed his Muslim faith after abandoning it in his 20s and 30s, his half-brother said.

The FBI is now reviewing hours of surveillance footage and hundreds of tips after the New Year's Day attack on Bourbon Street.

Officials in New Orleans, Louisiana, have been responding to questions on whether measures could have been taken to prevent an act of terrorism that killed 14 people and injured 35 on New Year’s Day.