 LONDON -- Pro-government forces pounded rebel-held Eastern Ghouta for the fourth day in a row Wednesday, killing at least 38 civilians, including four children, the Syrian Observatory for Human Rights, a U.K.-based monitoring group said.

Since Sunday night, Syrian and Russian airstrikes and shelling killed at least 310 civilians, including 72 children, in Eastern Ghouta, Rami Abdurrahman, the director of the Syrian Observatory for Human Rights, told ABC News.

“The warplanes are still in the sky,” Nour Adam, a media activist in Eastern Ghouta, who asked that his real family name be withheld out of safety concerns for family members in government-held territory, told ABC News on Wednesday. “People are in the shelters and shops are closed.”

An estimated 400,000 people are trapped in Eastern Ghouta with little access to food, water, fuel, electricity and health care, according to the UN. Many of them have left their homes and moved into underground shelters, where they spend their days and nights in hiding due to the intensity of the strikes.

The recent surge in violence in Eastern Ghouta, which has been besieged by the Syrian government since 2013, is part of President Bashar al-Assad’s campaign to seize Syria’s last remaining opposition-held territories.

On Monday and Tuesday, a total of 13 medical facilities were attacked in Eastern Ghouta, according to the Syrian American Medical Society. Three of SAMS’ medical staff in Eastern Ghouta were killed during those two days. One of them, a nurse, lost her life as she tried to escape the bombing on the hospital where she worked in the town of Arbin on Tuesday, SAMS said. Airstrikes continued to "relentlessly target the vicinity of the hospital for five hours, also directly hitting ambulances," SAMS said in a statement. At least 300 patients and medical staff were trapped in the hospital as staff moved patients to safer areas within the hospital, according to SAMS.

The United Nations secretary-general, Antonio Guterres, appealed on Wednesday for an immediate ceasefire in Eastern Ghouta, allowing humanitarian aid to reach people there. A truce should also allow the evacuation of an estimated 700 people who need urgent treatment outside of the besieged enclave, he said.

“I am deeply saddened by the terrible suffering of the civilian population in eastern Ghouta – 400,000 people that live in hell on earth,” he told the U.N. Security Council. “I know that very important consultations are taking place in this Council, aiming at a cessation of hostilities during one month in Syria, with a number of conditions, and of course I fully support that effort, but I believe eastern Ghouta cannot wait.”