The raids hit four makeshift hospitals in the besieged city, as well as a fifth in the nearby town of Atareb, the Syrian Observatory for Human Rights said Sunday.

The Independent Doctor's Association (IDA), a group of Syrian doctors that support clinics in Aleppo, allege that a two-day-old baby died after a government strike on a children's hospital. It was the second such strike on the same hospital in about nine hours, the organization said.

"After the second strike, we had to move him (the baby) downstairs to the bomb shelter, and that's why he died," said head nurse Malika. The baby allegedly died after his oxygen supply was cut during the bombing.

"The hospital is severely damaged and it's not the first time," she said in online conversations with IDA, the Agence France-Presse news agency reported.

IDA also posted a video online showing doctors carrying a tiny baby in a room lined with incubators and sandbags piled high just outside the entrance.

"Besiegement and the decimation of health care constitute war crimes. We demand an immediate end to and accountability for the collective punishment the city faces," IDA said.

According to the group, only five hospitals were left operating in the eastern part of Aleppo, which is under siege by the regime.

Syrian Red Cross chief Marianne Gasser said that news of the strikes filled her with "overwhelming despair."

"I think about the people who died, and keep dying, again and again. I think about the patients and their families. I feel for the doctors who want to help but can't anymore," she said.

Pro-regime forces blocked the main road into rebel-controlled parts of the country last week, intensifying their siege of Aleppo's rebel-held neighborhoods. Food and medical supplies are growing scarce according to residents.

Russia and the US have recently ended another round of talks on Syria, but kept most of the details secret. UN envoy to Syria Staffan de Mistura said he hoped to hold new peace talks in August.