The vast majority of Yemen's cholera deaths have occurred in areas controlled by Houthi rebels, largely the result of a blockade and air raids by the Saudi Arabia-led coalition they are fighting, an Al Jazeera investigation reveals.

An analysis of World Health Organization data shows that 1,794 of Yemen's 2,003 cholera deaths - 90 percent - have occurred in the northern and western governorates that are wholly or largely under the control of Houthi militiamen.

Houthi terrain has seen 84 percent of cholera infections - 456,962 out of 542,278 cases. Those infected have more chance of dying in rebel-held areas: 1.1 percent perish in Houthi-held Raymah, compared with 0.2 percent in government-held zones.

Rebel areas, together with parts of southern Yemen, also experience higher rates of hunger and have seen more hospitals and clinics bombed or shuttered since full-scale fighting erupted in March 2015.

Health and human rights experts told Al Jazeera while all factions in Yemen's war have caused civilian harm, the coalition's mightier firepower and control of sea and skies have skewed the health crisis into rebel-held terrain.

Dr Homer Venters, director of programmes for the research group Physicians for Human Rights, told Al Jazeera that coalition hits on clinics and sewage works were a Saudi "tactic of war" that amounted to the "weaponisation of disease".

Coalition attacks and a blockade on fuel and other supplies have left civilians in Houthi areas more vulnerable to cholera, and less able to get antibiotics and other life-saving help than those in other parts of the Arab world's poorest nation, he said.

"Aside from the devastation from air strikes on hospitals and clinics, the health emergency in Yemen has been made significantly worse by Saudi restrictions on petrol imports, leaving the remaining health centres without power," Venters said.

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Jonathan Kennedy, a Queen Mary University of London scholar, agreed. The concentration of cholera deaths on rebel-held land followed a devastating "human-induced collapse of the health and sanitation systems".

"It's a pretty good proxy for demonstrating the extent to which the Saudis have destroyed civilian infrastructure in Houthi-controlled areas, not just through bombs but also by the blockade of aid and other supplies," Kennedy told Al Jazeera.

He pointed to coalition attacks on health clinics, such as the August 2016 hit on a hospital in Houthi-held Hajja that killed 19 people. The fourth such attack on a Yemeni hospital backed by Doctors Without Borders (known by its French initials, MSF) led to the aid group pulling staff out of northern Yemen.

According to the International Committee of the Red Cross (ICRC), between March 2015 and March 2017, warring parties carried out more than 160 attacks on medical facilities and staff. Some 600 clinics were forced to close from March 2015 to March 2016, the United Nations said.

Closures have disproportionately affected civilians in rebel areas. The latest WHO data from October 2016 shows 37 percent of health facilities in mountainous Sadah have been damaged or destroyed, along with 28 percent in the area around the capital, Sanaa.

The air raids are intensifying. Yemen saw more attacks in the first half of this year than in all of 2016, said the Protection Cluster in Yemen, which works under the UN High Commissioner for Refugees (UNHCR). There were 5,676 attacks in the first half of 2017, up from 3,936 for all 2016.

Researchers faulted neither side, but Riyadh's Western-backed coalition has controlled Yemeni airspace since it joined the fight in March 2015. The United States has conducted some drone hits; the Houthis have no known air force.

Aid ships diverted

Charities also complain of coalition forces blocking commercial and aid ships in the Red Sea. Earlier this year, Save the Children protested that three vessels loaded with antibiotics and medical gear were stopped from unloading at Hudaida port, on a Houthi-controlled coast.

Ships have been diverted to Aden, a southern port that hosts the internationally recognised government and Saudi and Emirati troops, forcing aid teams to truck supplies north across risky battlefronts. Delays of drugs and fuel for hospital generators have affected rebel-held Sanaa and the northwest.

The Norwegian Refugee Council and other charities have urged the coalition, which controls Yemen's airspace, to permit flights to the country's main airport in Houthi-held Sanaa, to receive aid and allow sick and injured Yemenis to fly abroad for treatment.

Yemen's 30-month-old civil war pits President Abd-Rabbu Mansour Hadi's Saudi-backed government, which controls south and eastern Yemen, against the Iran-backed Houthis and other rebel groups in a shaky alliance with forces loyal to overthrown President Ali Abdullah Saleh.

Saudi officials acknowledge that cholera rates are higher on Houthi turf, but blame Houthi-led fighters for hitting hospitals, halting aid trucks, taxing petrol supplies and failing to cater to the needs of civilians.

"It's very clear from those [WHO] statistics that there is significant improvement in the regions followed by the legitimate government," Dr Abdullah al-Rabeeah, supervisor general of Riyadh's King Salman Humanitarian Aid and Relief Centre, told Al Jazeera.

"In the Houthi-controlled areas are the highest numbers because of the prevention of getting medical supplies going to the hospitals."

Onlookers agree with the Saudis, in part. Human Rights Watch (HRW) accused Houthis of laying banned anti-personnel mines and stopping food and aid bound for residents of besieged Taiz, Yemen's third-largest city.

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In an interview, Dr Sherin Varkey, deputy envoy to Yemen for the UN agency for children, UNICEF, repeatedly blamed "both sides" for causing civilian harm, but doubted that coalition actions had significantly exacerbated the cholera crisis.

"It has definitely contributed towards the outbreak, but outbreaks like this have multiple factors which contribute to their spread - whether it's population density, unhygienic conditions, the crumbling economy or rising levels of malnutrition," Varkey told Al Jazeera.

Aid groups and the UN typically remain neutral in wars and focus on peace talks and protecting civilians.

Other observers, however, have concluded that rebel Kalashnikovs and Soviet-era missiles cause much less damage than the Saudi-led coalition's F-15 fighter jets and 1,000kg, laser-guided Paveway IV bombs.

"The Houthis just don't have the military hardware to do the same kind of damage as the Saudi-led coalition," said Kennedy.

Kristine Beckerle, HRW's Yemen researcher, raised similar concerns.

"I don't know if it's intentional, but if you add the closure of Sanaa airport, the imposition of arbitrary and excessive restrictions on boats at Hudaida port, stopping journalists and human rights groups from going to Houthi-run areas, the bombing of hospitals - the net effect is that civilians in areas under Houthi control suffer," Beckerle told Al Jazeera.

The US and Britain provide arms and logistical assistance to the coalition. A high civilian death toll has caused controversy in Britain. Some US legislators have blasted Riyadh and tried to halt President Donald Trump's $500m arms sales to Saudi in June.

The war has killed more than 10,000 civilians and displaced three million people. There is no a diplomatic or military end in sight. Houthi leaders refuse even to meet the UN peace negotiator for Yemen, Ismail Ould Cheikh Ahmed.

Follow James Reinl on Twitter: @jamesreinl