GENEVA -- The charity Save the Children said a maternity hospital it supports in the opposition-held Idlib province in northern Syria was hit with three airstrikes.

One struck the entrance, killing two men who were waiting for their wives who were delivering, said AbdulKarim Ekzayez, health coordinator at Save the Children International.

He said reports from the hospital suggest six or seven people were injured, though he could not yet give precise figures. A lot of equipment, including incubators for newborns, was damaged.

The Britain-based Syrian Observatory for Human Rights said airstrikes in Kafr Takhareem village in Idlib hit a hospital and a center for civil defense volunteers. It said the hospital was no longer operational.

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The Observatory said an Islamist militant was believed to have been killed in the attack. Syrian state TV said government warplanes carried out an airstrike in the same area, also claiming a senior Islamist militant had been killed without naming him.

Amnesty International said the aerial attack "appears to be part of a despicable pattern of unlawful attacks deliberately targeting medical facilities," which can amount to a war crime.

Save the Children said the maternity hospital is the only such facility in the region, with the next facility some 44 miles away. The hospital opened in 2014 and has an on-call pediatrician and six incubators for premature babies.

The hospital serves an average of 1,350 women per month, spokeswoman Erin Taylor told CBS News.

Also Friday, the U.N. special envoy for Syria urged Russia to leave the creation of any humanitarian corridors around the embattled northern Syrian city of Aleppo to the United Nations and its partners.

"That's our job," said Staffan de Mistura as he explained his "suggestion" to Moscow at a press conference in Geneva, a day after Russia said its forces and those of the Syrian government would open humanitarian corridors around Aleppo and offer a way-out for civilians and surrendering fighters.

Meanwhile, Syrian activists said a U.S.-led coalition airstrike targeting a village in northern Syria held by the Islamic State of Iraq and Syria, or ISIS, had killed 28 civilians the previous night, including seven children.

Activists said that ISIS militants recaptured the nearby village of al-Bouweir on Thursday and killed 24 civilians.

In Geneva, de Mistura expressed support "in principle" for humanitarian corridors "under the right circumstances." He said he is awaiting clarification from Russian authorities about that plan, noting the urgent situation in the northern city, wracked by devastating violence in recent months.

The envoy also warned that "the clock is ticking for the Aleppo population."

"How do you expect people to walk through a corridor - thousands of them - while there is shelling, bombing, fighting?" de Mistura said.

He added that no one should be forced to leave Aleppo, but "indeed, some civilians may want to avail themselves of the possibility afforded by the corridor and by the Russian initiative. When they do, it is crucial that they be given the option of leaving to areas of their own choice."

De Mistura also praised a statement from the International Red Cross about the Russian proposal, which said any such corridors should have the "consent of all parties on all sides." ICRC regional director for the Mideast, Robert Mardini, said Friday he had no indication all sides were on board with the plan.

There were no reports of civilians using the corridors on Friday. Rebel fighters were forbidding people from using the Bustan al-Qasr crossing, in the north of the city, "out of fear for their safety," according to Khaled Khatib, a volunteer for the Civil Defense search-and-rescue brigade. He said civilians who leave the city risk being shot by government snipers or being detained because of their opposition sympathies.

"I haven't seen any family or people trying to cross," said Khatib.

Coalition airstrikes on the ISIS-held village of Al-Ghandour near the Turkish border killed 28 civilians Thursday, the Britain-based Syrian Observatory for Human Rights reported Friday. Observatory chief Rami Adurrahman said another 13 people were killed in the strikes but that he could not say if they were ISIS fighters or civilians.

Al-Ghandour is 15 miles northwest of the town of Manbij, a key hub in the extremist group's Syria network and a supply route to ISIS' de facto capital of Raqqa.

The international coalition had no immediate comment on the casualty figures reported by the Observatory. The bombings came a week after airstrikes, also blamed by Syrian activists on U.S. aircraft, killed at least 56 civilians in ISIS-held territory in northern Syria.

The Manbij area has seen extensive battles between ISIS extremists and U.S.-backed Kurdish-led fighters, who have been advancing under the cover of airstrikes by the U.S.-led coalition. The town is encircled by the Kurdish-led Syrian Democratic Forces.

The SDF were able to evacuate another 1,000 civilians from Manbij Thursday, according to Mustafa Bali, a local media activist living in the town of Kobani.

"There has been a lot of pressure on the militants in Manbij," said Bali.

After retaking the nearby village of al-Bouweir from the SDF on Thursday, ISIS extremists killed two dozen civilians, according to the Observatory.

Hamoud Almousa, a founding member of Raqqa is Being Slaughtered Silently, an activist group, said ISIS sought retribution from the village for "not defending Islam" when the SDF initially drove out ISIS earlier this summer.

Almousa said most of the villagers fled before the extremists retook al-Bouweir but the men who remained were killed.

Late Thursday, the U.S. Central Command, which is responsible for U.S. forces in the Middle East, said in a statement that the American-backed coalition had conducted airstrikes in the area of Manbij during the past 24 hours and that it was looking into whether an airstrike had resulted in civilian casualties.

It was not clear if the Manbij-area strikes that CENTCOM cited involved strikes on al-Ghandour.