Miami (AFP) - Florida saw a significant spike in murders after enacting a "Stand Your Ground" law allowing people to use lethal force in self-defense in public or on private property, international researchers said Monday.

The southern state's 24 percent rise in homicide from 2005 to 2014 stood in sharp contrast to nationwide homicide rates, which have been declining since the 1990s, according to research led by the University of Oxford and published in a special issue of the Journal of the American Medical Association (JAMA) Internal Medicine.

"This study highlights how Stand Your Ground is likely to be a cause of the rise in Florida murders, and provides crucial information which may influence future decision-making that affects wellbeing in the US and abroad," said co-author Antonio Gasparrini of the London School of Hygiene and Tropical Medicine.

Florida in 2005 became the first US state to broaden protections for those who use firearms for self-defense. A number of other states have since followed suit.

Before 2005, Florida state law said people could use firearms or other lethal force against home intruders if they believed they faced an imminent threat of death or serious injury.

The 2005 law, signed by then governor Jeb Bush, extended the law to provide individuals with immunity "for using lethal force to defend themselves in public places, as well as on private property."

Homicides linked to firearms rose 31 percent from 2005 to 2014, researchers found, compared to the previous sampling period from 1999-2004.

Overall, homicides in Florida for the decade after 2005 rose 24 percent, the study found.

The nightclub shooting in Orlando, where 49 people were killed -- making it the worst mass shooting in modern US history -- happened in June 2016 and was not included in the study.

"The findings are strong evidence that... this change to the law in Florida led to deaths that otherwise would not have occurred," said study co-author Douglas Wiebe at the University of Pennsylvania.

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"We need to think about the implications of these findings and Florida should consider reversing this decision that appears to have increased the use of lethal force."

All demographic groups were affected by the increases in homicide rates.

The largest proportional rises were seen in the 20-34 age group (which went up by 31 percent) and among the white population (which rose by 28 percent), the study said.

A 20 percent increase in homicides was found among African-Americans.

For comparison, researchers looked at homicide rates in four other states -- New York, New Jersey, Ohio and Virginia -- that had not enacted a Stand Your Ground law over the same period of time and found no increase in homicide rates.

Suicide rates in Florida were also unchanged, suggesting that other events such as the global financial crisis of 2007-9 was not the major factor associated with the rise in homicides in Florida.

- Little research -

Meanwhile, on a nationwide scale stronger gun laws were linked to fewer homicides using firearms, said a separate research paper in the same JAMA issue.

"Overall, we found evidence that stronger firearm laws are associated with decreased homicides due to firearms," said lead author Lois Lee, a doctor at Boston Children's Hospital's Division of Emergency Medicine and Harvard Medical School.

"Specifically, the laws that seemed to have the most effect were those that strengthened background checks and those that required a permit to purchase a firearm."

The research was based on articles in peer-reviewed journals from January 1970 to August 2016 that focused specifically on the connection between firearm homicide and firearm laws.

Researchers found just 34 studies that were rigorous enough to merit consideration, and they varied so much that only a general trend could be determined, not a specific reduction in the rate.

"One of our most important findings is the lack of high-quality research on this topic, especially in relation to the major health impact gun violence has had in this country," said co-author Eric Fleegler, also of Boston Children's Division of Emergency Medicine and Harvard Medical School.

"Much of the research really didn't have access to or use the highest quality data or analysis. The quality, number and time frame of these studies is very limited; many didn't study the laws over a long enough time to see the full effects of these types of laws."

The study blamed "limited federal funding for firearm-related research for the past 20 years" for the small amount of quality research.