Death Toll From Suspected US Raid in Syria Grows Amid Medical Crisis, Say Activists

— London -- The civilian death toll from suspected U.S.-led airstrikes in northern Syria earlier this week is rising sharply because of a lack of medical facilities to care for those wounded near the besieged city of Manbij, activists warn.

Yousef Houran, an activist and lawyer in nearby Aleppo, who co-founded The Syrian Institute for Justice, a nonprofit group that observes and documents cases of human rights violations in Syria, said he initially knew of about 63 civilian deaths resulting from Tuesday’s raids. But since then, many more have died, and the number of fatalities due to airstrikes on Manbij's al-Tukhar village is now more than 200, including 90 children, he said.

"The number is increasing because of the lack of hospitals or clinics," Houran told ABC News. "Most of the wounded civilians are dying because of the siege."

He said that civilians in the area had relocated to the northern part of al-Tukhar to seek shelter from airstrikes, where some 200,000 civilians are believed to be living under siege. Members of one family were afraid to stay in their home and were sleeping in a vehicle when they were killed in the airstrikes, he said.

ABC News has received photos purportedly from al-Tukhar taken by local activists after the airstrikes. Several show dead bodies of young children -- some appear to be toddlers.

Nearly two months ago, the Syrian Democratic Forces alliance, a U.S.-backed group of Arab and Kurdish fighters, launched an offensive against ISIS in Manbij and has besieged the town in an attempt to retake it from ISIS. Today U.S.-backed Syrian rebels gave ISIS 48 hours to leave Manbij, according to the AFP news agency.

Airwars, a nonprofit project that aims to document the international air war against ISIS and other groups in Syria and Iraq, listed on its website that 74 to 203 civilians were reported killed in the attack on al-Tukhar.

The numbers make the incident the largest loss of civilian life due to U.S.-led airstrikes in Syria, according to Amnesty International.

"One concern is that usually one would expect that a party to a conflict would be able to improve its civilian casualty, but it looks like the U.S.-led coalition is worsening, particularly in the Manbij area," Neil Sammonds, Amnesty International's lead researcher on Syria, told ABC News. "That's not acceptable. We have laws of war, and the U.S., like everyone else, must do all it can to abide by those laws. They must take all precautions to check if civilians are there and should not use weaponry which is likely to cause damage to areas where more civilians are likely to be killed. They should more closely check information that they are given about presence of civilians and not just assume that if they can't see civilians in a picture from the sky, there are no civilians there."

Amnesty International looked into 11 U.S.-led airstrikes over the last two years and found that they resulted in the killing of 250 to 300 civilians, but the U.S. recognized only five civilian deaths in those incidents, he said. In the past two years, at least 700 civilians have been killed by U.S.-led airstrikes, according to Sammonds, who said that the U.S. recognized only 24 civilian deaths by U.S.-led airstrikes for the same period.

In a statement to ABC News, U.S. Central Command said that it will investigate the reports of civilian deaths.

"We are aware of reports alleging civilian casualties near Manbij, Syria, recently. As with any allegation we receive, we will review any information we have about the incident, including information provided by third parties, such as the proximity of the location to [coalition] airstrikes, and any other relevant information presented. If the information supporting the allegation is determined to be credible, we will then determine the next appropriate step. We take all measures during the targeting process to avoid or minimize civilian casualties or collateral damage and to comply with the principles of the Law of Armed Conflict," the statement read.