Attacks on doctors and healthcare workers in conflicts from Somalia to Afghanistan have a drastic knock-on effect by jeopardising the health of millions, the International Committee of the Red Cross (ICRC) said in a report on Wednesday.

"Violence that prevents the delivery of healthcare is currently one of the most urgent, yet overlooked, humanitarian tragedies," Yves Daccord, ICRC director-general, said in a statement. "Hospitals in Sri Lanka and Somalia have been shelled, ambulances in Libya shot at, paramedics in Colombia killed, and wounded people in Afghanistan forced to languish for hours in vehicles held up in checkpoint queues. The issue has been staring us in the face for years. It must end."

According to Dr Robin Coupland, who led research carried out in 16 countries, millions could be spared if the delivery of healthcare were more widely respected.

"The most shocking finding is that people die in large numbers not because they are direct victims of a roadside bomb or a shooting," he said. "They die because the ambulance does not get there in time, because healthcare personnel are prevented from doing their work, because hospitals are themselves targets of attacks or simply because the environment is too dangerous for effective healthcare to be delivered."

In one case cited by the report, Health Care in Danger, Israeli forces prevented ambulance teams from reaching a house in the Zaytun neighbourhood that had been shelled during an offensive in Gaza in 2009. When the teams finally reached the house after disobeying soldiers' orders to turn back, they found four young children who had been crouching by the bodies of their mothers for four days.

The report cited several egregious attacks on healthcare workers. In 2009, a suicide bomber killed more than 20 people, most of whom had just graduated from medical school in Mogadishu, Somalia. The attack, the report said, not only prematurely ended the lives of young doctors - only the second batch of medical graduates in the past 20 years - but also destroyed any chance that tens of thousands of people might have had of receiving medical attention in the future.

A month later, the Puthukkudiyiruppu hospital in the Vanni region of northern Sri Lanka was shelled, suffering two direct hits, killing and wounding many of the 500 patients. Last April, Taliban insurgents in the southern city of Kandahar used an ambulance packed with explosives to kill 12 people at a police training base, the ICRC said.

Such incidents represent the tip of the iceberg, according to the ICRC, as attacks on healthcare facilities and personnel have become common in conflicts and upheavals around the world. Libya, for instance, has been affected by an exodus of healthcare professionals since unrest broke out early this year. Similarly, Iraq has reported that 18,000 to 34,000 doctors fled the country between 2003 and 2006.

The ICRC expressed particular concern at the long-term effects of attacks on medical personnel. The fight to eradicate polio has faced setbacks in countries such as Afghanistan, Pakistan and the Democratic Republic of Congo, where the safety of vaccination teams is difficult to assure.

"These disruptions to healthcare caused by violence are less visible and more difficult to measure than overt attacks against healthcare personnel and facilities," the report said. "But they are just as deadly for all the wounded and sick who never manage to reach the help they require."

The ICRC said the healthcare community alone cannot address the challenge.

"It is imperative that states, their armed forces but also others exercising authority recognise that violence that disrupts the delivery of healthcare is one of the most serious and widespread humanitarian challenges," it said.

Daccord called on parliaments and courts to ensure domestic legislation recognises the criminality of those who violate international humanitarian law and hold the perpetrators of violations accountable.

"Violence against healthcare facilities and personnel represents one of the most serious yet neglected humanitarian issues of today," he said. "Not only is it morally reprehensible, it is illegal under international law."