An upsurge in air strikes and ground attacks by Syrian regime forces against the besieged rebel-held enclave of Eastern Ghouta has killed at least 85 civilians since Dec. 31, UN human rights chief Zeid Raad al-Hussein said on Wednesday. "In Eastern Ghouta, where a crippling siege has caused a humanitarian catastrophe, residential areas are being hit day and night by strikes from the ground and from the air, forcing civilians to hide in basements," he said in a statement. Eastern Ghouta has been under regime siege since 2013 and its estimated 400,000 inhabitants are suffering severe shortages of food and medicine. The deadliest strikes on Tuesday hit the Hammuriyeh district, said the Syrian Observatory for Human Rights. The United Nations has said some 500 people are in critical condition inside Eastern Ghouta and need to be evacuated for urgent medical treatment. Twenty-nine patients, mainly children, were allowed out in December under a deal struck between the regime and rebels.