The Uniform Crime Reporting Program reports that the number of murders in the United States, from all causes (guns, knives, etc.) for the year 2004 was 16,100. That yielded a murder rate of 5.1 per 100,000 population. That rate has held true for the last several years, having fallen from a high of 24,000 per year.
Iceland has a population of approximately 300,000. There were fifteen murders in the country during the year 2005. That yielded an overall murder rate of 5 per 100,000.
The two rates then are 5.1 to 5. That's about as close as one can get statistically. If these rates are typical, then the U.S., which has 1,000 times the population SHOULD have about 1,000 times the number of murders that Iceland does.