WARNING: Graphic photos below
Human rights groups say US-led coalition airstrikes killed at least 56 civilians in and around the besieged city of Manbij in northern Syria on Monday and Tuesday.
The UK-based Syrian Observatory for Human Rights (SOHR) said 15 civilians were reportedly killed when airstrikes struck the city's al-Hazwanah neighborhood, and at least 41 died when when airstrikes hit the village of al-Tokhar, north of Manbij.
"Residents were fleeing the village... when the strikes hit," said SOHR's director, Rami Abdel Rahman.
The airstrikes were in support of the Syrian Democratic Forces (SDF), a US-backed militia, which is fighting to capture the city from Islamic State militants.
"Worrying accounts from local activists, as well as photos and video evidence, point to at least 60 civilian deaths in the July 18 airstrikes on al-Tukhar village, Manbij, in Aleppo governorate," Amnesty International said in a statement. "The true death toll may be difficult to document — according to media reports, members of local families were buried when the airstrikes leveled their clay and adobe homes."
Images circulating on social media purportedly showed victims of the airstrikes. VICE News could not independently verify the authenticity of the photos.
"We're tracking the worst ever week of alleged Coalition civilian casualties in 2 years of war," the civilian casualty watchdog Airwars Tweeted on Tuesday.
The deaths bring the total number of civilians killed in coalition airstrikes in the battle for the town to at least 104, including 29 children, SOHR said.
The US Department of Defense told VICE News the civilian casualty reports are being reviewed.
"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," the Pentagon said in a statement to VICE News. "If the information supporting the allegation is determined to be credible, we will then determine the next appropriate step."
In an earlier press release, the Pentagon said warplanes from the US led coalition conducted 18 airstrikes near Manbij on Monday, hitting "15 separate [Islamic State] tactical units and destroyed 13 [IS] fighting positions."
Amnesty International said the reports of more civilian deaths in Manbij showed that the US-led coalition "must redouble efforts to prevent civilian deaths and investigate possible violations of international humanitarian law."
"The bombing... may have resulted in the largest loss of civilian life by coalition operations in Syria," said Magdalena Mughrabi, interim deputy director of the Middle East and North Africa programme at Amnesty International. "There must be a prompt, independent and transparent investigation to determine what happened, who was responsible, and how to avoid further needless loss of civilian life."
The US military said in April that US airstrikes had killed 20 civilians and injured 11 others between September 2015 and April 2016 in Iraq and Syria. Airwars estimates that US and other coalition aircraft killed more than 900 civilians during the same period.
'The United States is responsible for almost every strike at Manbij," the group wrote on its website Tuesday. "According to official data, between May 22nd and July 17th this year 637 US airstrikes were carried out in Syria – with just 13 by its Coalition partners.
The Pentagon said Syrian rebels were continuing to battle Islamic State on four fronts for control of Manbij, and had captured an Islamic State headquarters located in a hospital. The coalition has carried out more than 450 airstrikes around Manbij since the operation to take the town began, the statement said.
Follow Benjamin Gilbert on Twitter: @benrgilbert
Reuters contributed to this report.