BEIRUT (Reuters) – Air strikes and shelling killed at least 25 people in rebel-held eastern Aleppo on Thursday on the third day of renewed bombing, a monitoring group said, and the mayor of the besieged sector warned of a total lack of fuel and food as winter encroached.

The bombardment of eastern Aleppo restarted on Tuesday after a weeks-long pause, part of a wider military escalation by the Syrian government and its allies, including Russia, against insurgents.

Moscow is using an aircraft carrier and missiles fired from  another warship against targets around Syria but says it is not bombing Aleppo. Syria’s government said on Tuesday it was striking what it called “terrorist strongholds” in the city.

The United Nations says 250,000 civilians remain in Aleppo’s opposition-controlled neighborhoods, effectively under siege since the army, aided by Iranian-backed militias and Russian jets, cut off the last road into rebel districts in early July.

Frequent air strikes on hospitals, and the disruption and pollution of water supplies, have worsened the humanitarian crisis. Medicines, food and fuel are all severely depleted.

“There is only enough to keep the bakeries going to give people at least some bread. People are only getting about 15 percent of what they need,” Brita Hagi Hassan, president of the city council for opposition-held Aleppo, told Reuters.

Hassan is outside eastern Aleppo and cannot return because of the siege but he is still running the council remotely, he said.

International charity Oxfam said it had moved a large electricity generator to the Suleiman al-Halabi water station that is located on the frontline between east and west Aleppo and still serves both sides of the city under an agreement.

It said all other aid to the besieged area remains cut off.

The Syrian Observatory for Human Rights, a British-based organization that monitors the war, said shelling and air strikes from helicopters and jets hit the eastern half of the city, causing severe damage. Air strikes also hit rebel-held areas west and south of Aleppo.

Shelling of government-held western Aleppo by rebels during a failed counter-attack they staged earlier this month killed dozens of people, the United Nations said.

Syria’s civil war pits President Bashar al-Assad against mainly Sunni rebels seeking to oust him. It has cost hundreds of thousands of lives and displaced around half the country’s pre-war population since it began in 2011.

(Reporting by Lisa Barrington; Editing by Angus McDowall and Mark Trevelyan)