20,000 Syrians have fled east Aleppo this week: Red Cross

The aid agency said it stood ready to organise medical evacuations of the sick and wounded and called for civilians to be allowed safe passage out of the besieged eastern sector.

The ICRC called again for access to east Aleppo, which it has not been able to reach with food, medicines and other relief supplies since April.

Syria and its allies aim to drive rebels from Aleppo before Donald Trump takes office as U.S. president, a senior official in the pro-Damascus military alliance said, as pro-government forces surged to their biggest victories in the city for years.

"With no end in sight to the fighting or indeed a wider peace being reached, thousands more civilians face a daily struggle to survive," said Marianne Gasser, head of the ICRC delegation in Syria, who is currently visiting shelters for the newly displaced staying in government-controlled west Aleppo.

"The needs are massive, and the ongoing fighting and insecurity make aid deliveries and repairs difficult," she said, noting that the ICRC and Syrian Arab Red Crescent (SARC) were helping to dig wells to provide water.

More than 40,000 people have fled areas of fighting in western Aleppo, the ICRC said, bringing the total who have left Syria's biggest pre-war city to 60,000 since August.