One-month-old conjoined twins evacuated from a besieged area near Damascus died Wednesday in the capital, despite a campaign to send them abroad for surgery, the Syrian Arab Red Crescent said.

"The died on Wednesday and they will be buried tomorrow in Damascus in the presence of their mother," spokeswoman Mona Kourdi told AFP.

The two boys, Moaz and Nawras, were joined at the chest.

They were evacuated on August 12 from Eastern Ghouta, which is besieged by Syrian government forces, after a campaign on Twitter under the hashtag #Evacuatethetwins.

Born in the rebel-held district of Hammuriyeh, the twins were admitted to hospital in Damascus awaiting their transfer abroad for possible life-saving surgery.

"They suffered from heart and liver defects and... were in a severe state of health," the Red Crescent said in a statement.

Katoub Mohamad of the Syrian American Medical Society (SAMS) charity accused the Syrian authorities of delaying their transfer.

"We received several offers from hospitals and physicians... to help the twins... but the problem was the transfer," Mohamad told AFP from Turkey.

"The foreign ministry did not authorise the babies to travel without passports, while SAMS was informed by the State Department that the US was ready to receive them without documents," he said.

Kourdi denied this, saying "the delay was due to their health condition".

The Red Crescent said the passports had been delivered to those caring for them and "that official approval was secured after an Italian hospital had agreed to receive them."

Syria's five-year conflict has taken a heavy toll on children, with thousands living in besieged areas subject to air strikes and shortages of food and other essentials.

Last week, the image of four-year-old Omran covered in blood and dust went viral online after his rescue from a bombed-out building, symbolising the fate of children in the devastating war.