BEIJING, Aug. 29 (Xinhuanet) -- Every 10 U.S. citizens own nine guns, making the country the most heavily armed in the world.

U.S. citizens own 270 million of the world's 875 million known firearms, according to the Small Arms Survey 2007 by the Geneva-based Graduate Institute of International Studies Tuesday.

Of the 8 million new firearms manufactured annually around the world, about 4.5 million are bought in the United States.

"There is roughly one firearm for every seven people worldwide. Without the United States, though, this drops to about one firearm per 10 people," it said.

On a per-capita basis, Yemen has the second most heavily armed citizenry behind the United States, with 61 guns per 100 people.

The report, which relied on government data, surveys and media reports to estimate the size of world arsenals, estimated there are 650 million civilian firearms worldwide, and 225 million held by law enforcement and military forces.

Five years ago, the Small Arms Survey had estimated there were a total of just 640 million firearms globally.

"Civilian holdings of weapons worldwide are much larger than we previously believed," the director of the Geneva-based group, Keith Krause, told reporters.

Only about 12 percent of civilian weapons are thought to be registered with authorities, the report said.