WASHINGTON - There have been renewed calls for stricter gun control in the United States following the shooting deaths last week of 14 students and three adults at a Florida high school.
Here's a look at some of the issues surrounding gun control and various proposals:
Assault weapons ban
Semi-automatic weapons such as the AR-15-style rifle used by Parkland, Florida school shooter Nikolas Cruz were prohibited under the 1994 federal assault weapons ban passed by Congress and signed into law by President Bill Clinton.
It prohibited the manufacture and sale of the weapons for civilian use and also limited "large-capacity" magazines -- defined as those capable of holding more than 10 rounds.
The ban lapsed in 2004 amid pressure from the powerful National Rifle Association and congressional efforts to renew the prohibition since then have failed.
Democratic Senator Dianne Feinstein of California introduced an assault weapons ban following the massacre of 26 people -- 20 of them young children -- at Sandy Hook elementary school in Newtown, Connecticut, in December 2012.
It did not pass and Feinstein re-introduced an assault weapons ban in November 2017 after 26 people were shot dead at a church in Texas.
It also has gone nowhere.
Fifty percent of those surveyed in a Washington Post-ABC poll after the Parkland shooting supported a nationwide ban on the sale of assault weapons.
Forty-six percent were opposed.
Expanded background checks
The White House has said following the Florida school shooting that President Donald Trump supports efforts to improve the federal background check system for gun buyers.
The 1993 Brady Bill requires federally licensed gun dealers to run background checks on purchasers with the FBI.
The names of potential buyers are run through a database called the National Instant Criminal Background Check System (NICS), which is meant to flag those prohibited from buying firearms, such as convicted felons, domestic abusers and the dangerously mentally ill.
There are a number of state loopholes, however, and many private sales are unregulated.
A bill co-sponsored by Republican Senator John Cornyn of Texas and Democratic Senator Chris Murphy of Connecticut seeks to ensure greater compliance by state and federal agencies with NICS.
This is the bill that the White House said Trump is considering supporting and it has also received the backing of the NRA.
Cornyn and Murphy introduced the legislation after the Sutherland Springs, Texas, church shooting because the Air Force had failed to inform NICS that the gunman had a conviction for domestic abuse that would have prevented him from buying the guns he used.
One of the more controversial proposals raised by NRA lobbyists is to arm teachers.
Forty-two percent of those surveyed in the Washington Post-ABC poll said this could have prevented the Parkland shooting.
Fifty-one percent said it could not.
The partisan divide in the United States is also reflected in support for the move to arm teachers.
Fifty-nine percent of Republicans surveyed said they believed allowing teachers to carry guns could have prevented the Parkland shooting.
Only 23 percent of Democrats thought so.
After a shooting in Las Vegas last October that left 58 dead -- the deadliest mass shooting in modern US history -- calls went out for a ban on an accessory known as a "bump stock."
Bump stocks allow semi-automatic weapons to fire like automatic weapons and Las Vegas shooter Stephen Paddock had affixed them to some of his weapons as he rained gunfire on an outdoor concert from his hotel suite.
Several states have already banned bump stocks and Feinstein has introduced legislation that would prohibit the devices.
The prohibition has drawn some Republican support.
But a number of members of Congress have said the ability to regulate bump stocks already exists with the Bureau of Alcohol, Tobacco and Firearms (ATF) and that it needs to enforce the current restrictions.
Mental health screening
One thing both Republicans and Democrats agree on is that better mental health screening could help prevent gun violence.
Parkland shooter Nikolas Cruz was a troubled teenager, according to numerous accounts, and his disturbing behaviour was brought to authorities' attention on numerous occasions.
The 19-year-old Cruz had nevertheless legally acquired several deadly weapons.
The FBI even received a warning about a month before the attack that Cruz had acquired guns and may have been planning a school shooting. No action was taken.
Seventy-eight percent of the Democrats in the Washington Post-ABC poll said more effective mental health screening and treatment could have prevented the Parkland attack.
Seventy-seven percent of Republicans agreed.
While efforts are being made to expand background checks and to restrict access to certain types of guns, the NRA is seeking at the same time to loosen regulations.
One such effort would allow gun owners who have a permit to carry a concealed weapon in one state to legally bring that weapon into another state.
The Concealed Carry Reciprocity Act was passed by the House of Representatives by a 231-198 vote in December 2017 but has yet to clear the Senate.