"Pro-Russian insurgents' attacks on medical units and personnel are putting sick and vulnerable people and those who care for them at risk," Yulia Horbunova, Europe and Central Asia researcher at Human Rights Watch (HRW), said in a statement.
"This appalling disregard of people who are sick or wounded can be deadly and needs to stop immediately."
The New York-based rights group said it had documented insurgents hijacking ambulances to transport fighters, coercing medics and expropriating equipment in what could constitute war crimes in Ukraine's civil conflict.
Medical services were not only suffering at the hands of the rebels: at least two medics have been killed as rockets or mortars likely fired from government positions hit five hospitals in rebel-held territory, HRW said.
Rebels have stationed significant numbers of fighters at hospitals, making them possible targets for attack, and have seized wards in at least two hospitals for treating injured insurgents, the statement said.
The United Nations estimates some 1,150 people have been killed and around 3,450 injured in the brutal fighting tearing apart the industrial heartland since April.
The Red Cross has said Ukraine is now in a civil war -- a classification that would make parties in the conflict liable to prosecution for war crimes.
Civilians have borne the brunt of the violence with both Ukraine's army and insurgent fighters accused of firing heavy weapons in built-up areas.
The United Nations says that over 100,000 people have fled to other regions of Ukraine while Russia claims that more than 500,000 have crossed its border in search of refuge.
Water, electricity and food supplies have been severely disrupted in besieged rebel-held cities, with local authorities now warning of a "humanitarian catastrophe" in some areas.
Fuel supplies have also been exhausted in some rebel areas meaning that overstretched medical services are struggling to reach civilians injured in the fighting.
HRW's allegations come as fears of brutal street-to-street combat grow with Ukraine's military closing in on the main rebel stronghold of Donetsk after a string of advances over the last month.
Local authorities said the sound of heavy fire was heard around the city overnight and eight rebel fighters were wounded when they were hit by an explosion.
Ukraine's military top brass have pledged to stamp out the insurgency in the near future, but rebels have hunkered down in major population centres and pledged to fight to the death.