One of the main hospitals in Syria's northern city of Aleppo has been forced to close indefinitely after being targeted by rockets and barrel bombs, a humanitarian group says.

Doctors Without Borders (MSF) said on Monday the private Al-Sakhour hospital, serving around 400,000 people as one of the only hospitals in east Aleppo, halted all activities after being bombed twice on consecutive days last week.

"It is unclear when or if the hospital will be operative again" as it was severely damaged, an MSF statement said.

The hospital's staff are Syrian, but it receives medical equipment from MSF every three months, an MSF representative told AFP.

"The next delivery was supposed to be in June, but we don't know if it will happen," he said.

Raquel Ayora, MSF's director of operations, said: "We renew our appeal to the warring parties to respect civilians, health facilities and medical staff.

"These new attacks on medical infrastructures are intolerable."

According to the Syrian Observatory for Human Rights, barrel bombs -- crude weapons made of old containers packed with explosives -- struck near the hospital on April 28 and 30.

MSF said another medical centre in Aleppo closed on April 17 after being repeatedly targeted, and that an air attack on an ambulance last month killed three medical staff, their driver and a civilian.

Al-Sakhour hospital was also forced to close for several weeks last summer after air strikes on it, MSF wrote.

In the past, MSF has said "the complexity and danger" of providing aid during the Syrian conflict "are at the highest possible level".

The group has been forced to rein in its efforts in the war-torn country since it has no authorisation to operate in government-controlled areas and no viable go-betweens with representatives of the complex rebel opposition.

The MSF statement said it feared that increased fighting in the northern provinces of Aleppo and Idlib would lead to further attacks on hospitals and medical centres "to increase the suffering of the population".

Once Syria's economic powerhouse, Aleppo city has been split between regime control in the west and rebel control in the east.

Government and opposition forces regularly exchange fire which often kills civilians.