Moves to tighten gun laws in the US are facing a backlash from sheriffs in rural communities who are refusing to uphold new restrictions by declaring their counties "Second Amendment Sanctuaries".

The wave of mass shootings, notably at the Marjory Stoneman Douglas High School in Parkland, Florida, where 17 pupils and staff were killed last February and two survivors committed suicide this week, has prompted state legislatures to pass a raft of measures.

New laws have included including compulsory background checks, a ban on assault weapons and raising the minimum age for gun ownership.

With Democrats making sweeping gains at local level in last year's mid-term elections, the pace of new legislation has intensified.

Nevada is set to debate a comprehensive firearms control bill which will make modifying a weapon a criminal offence and allow localities to create "gun free" zones.

Arizona and Arkansas are also currently considering "red flag" bills which would allow weapons to be confiscated from owners who are considered dangerous.