Kinshasa - Roadblocks in war-torn areas of Central African Republic and Democratic Republic of Congo provide armed groups with millions of dollars in annual income, a report said on Wednesday.
A year-long study by the International Peace Information Service (IPIS), a Belgian research group, found 1 082 roadblocks in CAR and in the North and South Kivu provinces of eastern DRC alone.
Money extorted from road users nets armed groups around $8.2m annually, it estimated.
Roadblocks are a "key mechanism of conflict funding," IPIS said in a statement.
"Strangling development and livelihoods, attracting violent confrontations and generating millions in revenues, roadblocks are as crucial to continuing conflict in Central Africa as natural resources."
According to the study, armed men were present at 73% of roadblocks.
Investigators mapped 284 roadblocks in CAR, where violence has raged since 2013 between factions of mostly Christian militias known as anti-Balaka and the Muslim-majority Seleka rebels.
Seleka rebels control most of the roadblocks in CAR - set up every 24km - collecting about six million euros in taxes annually, IPIS found.
They make most of their money taxing cattle and Sudanese coffee traders, it said.
Only 115 roadblocks where operated by government agents.
In the eastern region of DRC, the inquiry found 798 roadblocks set up at average intervals of 18km. Of these, 569 were operated by government agents.
The area has been the scene of inter-ethnic violence for the past 20 years, as groups clash for control of mining and other resources.
Truckers in North Kivu alone are shaken down at roadblocks to the tune of about a million euros annually.
"Finding a Congolese road without a roadblock is a challenge - basically, everything that moves, is taxed," said Peer Schouten, IPIS research coordinator and the study's lead author.
"Women going to market, farmers accessing fields, traders taking to the road... We were surprised at the sheer density of roadblocks. They indicate the extent of structural extortion in DRC. And it's the people that suffer."
"Its time for the international community to broaden its scope beyond conflict minerals," Schouten said.