United Nations Secretary-General Ban Ki-moon condemned rebels Friday for cutting water supplies to the besieged northern Syrian city of Aleppo, calling for services to be restored immediately.

Ban's office said water supplies had been cut for eight days, depriving at least 2.5 million people of access to water safe for drinking and sanitation.

Al-Qaeda's Syrian branch, Al-Nusra Front, was among the rebel groups that cut the supplies, though the Red Crescent said that some services had been restored.

Ban "notes that preventing people's access to safe water is a denial of a fundamental human right," his office said.

"Deliberate targeting of civilians and depriving them of essential supplies is a clear breach of international humanitarian and human rights law."

Ban called on all parties to "ensure that the water supply in Aleppo -- and everywhere in Syria -- is permanently restored and to refrain from targeting civilian facilities and infrastructure," the statement added.

Rebel rocket fire killed 13 people in Aleppo earlier, while troops launched an offensive on rebels in Daraa province of southern Syria, state media said.

The Syrian Observatory for Human Rights also reported the bloodshed in Aleppo and said a large-scale army operation was under way in Daraa for control of hills held by rebels.