Image copyright SPL Image caption There are more than 300 million firearms in the US

Researchers claim a new study provides some of the most compelling evidence yet for tighter gun controls in the US.

The team followed the consequences of the State of Missouri repealing its permit-to-purchase handgun law in 2007.

The law had required purchasers to be vetted by the local sheriff and to receive a licence before buying a gun.

Reporting soon in the Journal of Urban Health, the researchers will say that the repeal resulted in an immediate spike in gun violence and murders.

The study links the abandonment of the background check to an additional 60 or so murders occurring per year in Missouri between 2008 and 2012.

"Coincident exactly with the policy change, there was an immediate upward trajectory to the homicide rates in Missouri," said Prof Daniel Webster, director of the Johns Hopkins Center for Gun Policy and Research.

"That upward trajectory did not happen with homicides that did not involve guns; it did not occur to any neighbouring state; the national trend was doing the opposite – it was trending downward; and it was not specific to one or two localities – it was, for the most part, state-wide," he told BBC News.

The team said it took account of changes that occurred in policing levels and incarceration rates, trends in burglaries, and statistically controlled for other possible confounding factors such as shifts in unemployment and poverty.

Media playback is unsupported on your device Media caption Prof Daniel Webster: "Non-licensed gun dealers could sell a handgun with no questions asked"

What was stark, added Prof Webster, was the rise in the number of handguns that subsequently found their way into the hands of criminals.

The team counted a doubling of handguns shortly after sale being recovered from scenes of crimes or from criminals.

"This study is compelling confirmation that weaknesses in firearm laws lead to deaths from gun violence," said Prof Webster.

The Johns Hopkins researcher was participating in a discussion here at the annual meeting of the American Association for the Advancement of Science (AAAS).

The theme was "science-based strategies for reducing gun violence".

America currently has more than 300 million firearms in circulation. But the issue of gun control remains a hugely contentious one.