Human Rights Watch said Sudanese security forces have used live ammunition and rubber bullets to disperse protesters, opposition members and some members of the media.
Protests erupted last week out of frustration with austerity measures in Sudan. The oil-dependent economy in Khartoum was strained when South Sudan gained control over most of the country's oil fields last July.
The rights organization called on the Sudanese government to end its crackdown on opponents.
U.S. State Department spokeswoman Victoria Nuland said force wasn't the solution to economic problems.
"The heavy-handed approach adopted by Sudanese security forces is disproportionate and deeply concerning," she said in a statement. "Sudan's economic crisis cannot be solved by arresting and mistreating protesters."
Sudan and South Sudan were pushed to the brink of war early this year following disputes over oil fields near their shared border.
Nuland said serious bilateral negotiations were needed to stem the crisis.
"Sudanese authorities need to rein in their security forces immediately and protect protesters from vigilantes," Daniel Bekele, Africa director at Human Rights Watch, said in a statement.