It says starvation and disease caused by a conflict, which began in 1998, were by far the greatest killers.

The results of the study, conducted by the International Rescue Committee, a New York-based relief agency, are published in the British medical journal The Lancet.

"Congo is the deadliest crisis anywhere in the world over the past 60 years," said Richard Brennan, the study's main author. "Ignorance about its scale and impact is almost universal and international engagement remains completely out of proportion to humanitarian need." The committee found that Congo's war claimed 38,000 lives every month in 2004.

Researchers visited 19,500 households across the vast country over three months last year and recorded the number of deaths experienced by families. They found that, of every 1,000 people, 2.1 died every month. This compared with a pre-war mortality rate of 1.5 in every 1,000. Assuming war to be the sole cause of the increase in death rates, the study said the conflict has claimed 3.9 million lives, with the numbers rising each month. Civil war began when Uganda and Rwanda invaded Congo, ostensibly to hunt down rebel groups.

Both countries looted its mineral wealth and fighting escalated when five other African nations sent in their troops.