Families of victims in the 2012 Sandy Hook school massacre filed a US lawsuit Monday seeking damages from the manufacturers of the high-powered assault rifle used in the slaughter.

The lawsuit was lodged a day after the two-year anniversary of the horrific shooting that claimed the lives of 26 people, among them 20 young children.

The suit aims to hold the makers of the deadly AR-15, Bushmaster, liable for wrongful death and negligence.

It says 20-year-old killer Adam Lanza would never have been able to carry out his 264-second attack if he had not had access to a high-capacity weapon which had been "specifically engineered" for the United State military for use in combat.

"The number of lives lost in those 264 seconds was made possible by the shooter's weapon of choice: a Bushmaster AR-15 Rifle, model XM15-E2S," the lawsuit alleged.

"The AR-15 was specifically engineered for the United States military to meet the needs of changing warfare," said attorney Josh Koskoff, representing the families.

"One of the Army's specifications for the AR-15 was that it has the capability to penetrate a steel helmet. This weapon was not designed for home defense or hunting.

"This weapon was designed to efficiently kill other human beings in combat."

Nine families who lost a child or an adult during Lanza's rampage at Newtown on December 14, 2012 have joined the lawsuit. Natalie Hammond, a teacher who was shot but survived the assault, has also joined the case.

Sandy Hook, which took place just before Christmas and whose victims were mostly children aged between six and seven, shocked America and reignited the national debate about gun control in the United States.

However moves to introduce a modest tightening of gun control laws foundered in Congress despite overwhelming public support.

The suit lodged on Monday also seeks damages from Camfour, an arms distributor based in Massachusetts, and Riverview Gun Sales, the Connecticut shop where Lanza's mother bought the weapon used in the attack in March 2010.