Human remains have been found at the site of the Nashville vehicle explosion, authorities have said, even as more evidence emerged signaling a planned attack. The recreational vehicle exploded in the early hours of Christmas morning on Friday, injuring at least three people. Police now say more people could have been injured.

Nashville police Chief John Drake said the tissues found at the site will be examined to confirm if they are human remains. It is not clear if it belonged to a victim or the perpetrator of the attack.

Immediately after the blast the local authorities said it was a deliberate act. Besides the ATF, the FBI is also investigating the incident. Mayor John Cooper said the blast was caused by a "deliberate bomb."

Meanwhile, police said they could evacuate a significant number of people as they identified a voice message from the parked vehicle, warning that a bomb was about to explode. According to the police, the van was blaring a recorded warning that a bomb would explode within 15 minutes.

Nashville Explosion

"If you can hear this message, evacuate now," the recorded message said, seconds before the explosion. However, no blast happened at the end of the countdown, and people returned to the site. That's when the bomb went off, injuring people and damaging more than 40 establishments.

The police said a female voice was speaking in the warning message. "There were a number of people who did evacuate and then we know of some people, it didn't go off when the message said it would and so people started coming back in, and then it went off," Nashville Vice Mayor Jim Shulman told CNN.

Police have no information about who might have been inside the vehicle at the time of the blast. Police were alerted about a suspicious vehicle parked outside the AT&T building about 6 am. Even as the hazardous devices unit of the police reached the spot, the explosion happened. Remains of a recreational vehicle were seen at the spot of the blast.

"The explosion was significant, as you can see ... the police department, its federal partners — the FBI and ATF — are conducting a large-scale investigation to this point ... ," Nashville police spokesman Don Aaron said, according to the NY Post.