US Justice Department will conduct a "Critical Incident Review" of law enforcement's response to the shooting amid criticism over why police failed to swiftly confront the gunman.

The review was requested by Uvalde Mayor Don McLaughlin.
The review was requested by Uvalde Mayor Don McLaughlin. (AP)

The United States Department of Justice will conduct an independent review of the police response to the recent mass shooting at a Texas elementary school.

The decision on Sunday comes amid mounting questions over security personnel's failure to stop the gunman as he attacked the Robb Elementary School on Tuesday.

"The goal of the review is to provide an independent account of law enforcement actions and responses that day", said DoJ spokesman Anthony Coley in a statement.

It will also "identify lessons learned and best practices to help first responders prepare for and respond to active-shooter events," Coley added.

The review was requested by Uvalde Mayor Don McLaughlin and "will be fair, transparent and independent", he said.

READ MORE: US police under fire over 'late' response to Texas school massacre

Slow reaction

On Tuesday, a teen gunman stormed Robb Elementary School in the small Texas town of Uvalde, killing 19 children and two teachers.

The incident was the latest in an epidemic of deadly mass shootings in the United States.

In the wake of the shooting, the behaviour of the police has come under severe scrutiny as accounts emerge of their slow reaction.

Texas authorities admitted on Friday that as many as 19 police officers were in the school hallway for nearly an hour before breaching the room the gunman was in and killing him.

Authorities said the officers mistakenly thought the assailant had stopped killing and was now barricaded.

Officials now call this delay a "wrong decision" but parents have expressed fury.

READ MORE: Texas gunman shot grandmother first before killing students: police

Source: AFP