US law enforcement and intelligence agencies are concerned about copycat vehicle-ramming attacks following the New Year's Day attack in New Orleans by a US Army veteran, according to a US law enforcement intelligence bulletin published on Friday.

Such attacks "are likely to remain attractive for aspiring attackers given vehicles' ease of acquisition and the low skill threshold necessary to conduct an attack," said the bulletin issued by the FBI, the Department of Homeland Security and the US National Counterterrorism Center and reviewed by Reuters.

The FBI on Thursday said Shamsud-Din Jabbar, a 42-year-old Texas native, was "100 percent inspired" by the Islamic State terrorist group to ram a truck into New Year's Day revelers in New Orleans, killing at least 14 people and injuring dozens of others.