A United States Senate panel has approved a Democratic bill that would ban assault weapons and high-capacity gun magazines.
The party line vote was taken three months to the day after a school massacre in Newtown, Connecticut, in which a gunman killed 20 young children and six adults before taking his own life.
The Senate Judiciary Committee voted 10-8 for the bill, seen by many as the most problematic element of President Barack Obama's push to reduce weapons violence by tightening up Americans' almost unfettered access to firearms.
The assault weapons measure - as well as three other items approved earlier in the package of proposed gun reforms - would result in the most substantial change to US gun legislation in a generation.
However, the measures face an uphill battle, meeting with stiff opposition not just from Mr Obama's Republican foes in Congress, but from many conservative-leaning Democrats as well.
The semi-automatic Bushmaster XM15 rifle used in the Connecticut shooting is the sort of high-powered, automatic firearm that would be prohibited if the bill were to become law.