BEIRUT // Residents of Syria’s second city Aleppo have been without water for a week because Islamist fighters have cut supplies into rebel and regime-held areas, a monitoring group said on Saturday.

The Syrian Observatory for Human Rights said the Al Qaeda affiliate Al Nusra Front had cut water supplies from a pump distributing to both the rebel-held east and government-held west of Aleppo.

Last month, opposition forces cut the electricity supply to regime-controlled areas of Aleppo and the surrounding countryside.

But the director of the Observatory, Rami Abdel Rahman said, the groups were unable to cut off water supplies to regime areas without also affecting rebel-held neighbourhoods, calling the move “a crime”.

Once home to about 2.5 million residents and considered Syria’s economic powerhouse, Aleppo has been divided between government and opposition control since shortly after fighting there began in mid-2012.

At least one million people have been displaced from the city since then by fighting and relentless regime aerial bombardments of rebel areas.

Opposition forces also regularly shell regime-held parts of the city in the west.

The Observatory said the week of water cuts had forced residents to queue at wells to collect water, and the Britain-based group warned that some people were drinking unclean water, risking a spread of disease.

Meanwhile, more than 100,000 civilians have fled the eastern Syrian province of Deir Ezzor because of fierce clashes between rival Islamist groups, the Observatory said.

The group said the clashes between Al Nusra Front and the rival Islamic State of Iraq and the Levant (ISIL) had killed 230 militants in the past 10 days.

Of those, 146 were members of Al Nusra and other Islamist brigades, including some who were executed by ISIL.

The clashes between the two groups in the oil-rich province began at the end of April and come after a wider backlash against ISIL that started in January.

ISIL, which grew from Al Qaeda’s Iraq branch, has been the target of a joint campaign by moderate and Islamist rebels as well as Al Nusra since early January.

The campaign has pushed it out of much of Aleppo and Idlib provinces, though it has strengthened its presence in the provincial capital of Raqa province.

ISIL was initially welcomed by some of the Syrian opposition, but its abuses of civilians and rebel forces sparked the backlash that begin this year.

In February, ISIL withdrew from most of Deir Ezzor under pressure, but in recent weeks it has advanced once again, the Observatory said, regaining territory in the west of the province.

The infighting among rebel groups has detracted from their objective of overthrowing the Syrian president, Bashar Al Assad, whose forces have been making gains across the country in recent months.

In a significant victory for the regime ahead of presidential elections on June 3 that Mr Al Assad is expected to win easily, most of the rebel forces in the central city of Homs left last week after holding out against a siege for nearly two years.

On Saturday, hundreds of former residents streamed back into the devastated Old City of Homs, picking through the ruins of their homes after rebels left the area.

They walked, rode bicycles and motorbikes, and pushed strollers down streets strewn with rubble.

Every building bore signs of the conflict, from bullet holes to enormous craters created by the shells that struck almost daily during the nearly two-year siege.

Many were visibly emotional at the sight of their former neighbourhoods, now rendered almost unrecognisable.

“The destruction is just horrible,” said Rima Battah, 37, in the Hamidiyeh district of the Old City.

A final convoy of rebels withdrew from the Old City on Friday, handing control of all but one district of Homs to the government under a deal negotiated between the regime and opposition forces.

As the rebels left, government troops swept the evacuated neighbourhoods for explosives.

The governor of Homs, Talal Barazi, told the state news agency Sana that the areas were now “safe and free of weapons and insurgents thanks to the sacrifices of the Syrian army”.

State television also carried live footage of the influx of residents, interviewing people who offered their thanks to the army and Mr Al Assad.

* Agence France-Presse