Dozens of civilians have been killed in US-led air strikes against areas in Syria held by the Islamic State of Syria and the Levant group (ISIL, also known as ISIS), a monitoring group said.

At least 56 civilians, including 11 children, were killed in air strikes on the Tokhar area in the northern city of Manbij in the Aleppo governate on Tuesday, according to the Syrian Observatory for Human Rights.

Ten others, including four children, were killed in coalition strikes on the village of Hamira, in the southern suburbs of Manbij.

The UK-based Observatory has put the total number of civilians killed by coalition strikes on Manbij since the Democratic Forces of Syria (DFS) launched their campaign there at the end of May, at 167.

Among the dead were about 44 children, 17 women and eight prisoners, the Observatory said.

"The US central command has confirmed to Al Jazeera that it was conducting air strikes in the area and says it needs to investigate allegations of whether civilians were injured or killed in this incident," Al Jazeera's Rosiland Jordan, reporting from Washington, said.

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Director of the Observatory Rami Abdel-Rahman told German news agency DPA: "We believe that the raids which were carried out Tuesday were by US [or] allied planes, but it was by mistake."

Residents in the area say the death toll could be upwards of 200.

"It seems that the Syrian Democratic Forces under the leadership of the International coalition which is in charge of planning have decided to adopt a scorched earth policy," Hasan al-Nifi, a community leader in Manbij, told Al Jazeera.

"Manbij is full of residents, a quarter of a million residents, used by ISIL as human shields. Yesterday the coalition struck al-Zahuna neighbourhood, where more than 23 people were killed. Then it struck the western gate of the city, killing people.



"Today the residents of Tokhar woke to a horrific massacre. The death toll rose to 212 and the numbers are rising."

The Manbij area has seen intense US-led air strikes in support of Kurdish-led forces who are trying to seize the city from ISIL, so as to block the armed group's access to the nearby Turkish border.

The SDF, an alliance of Arab and Kurdish fighters backed by the US, launched an offensive against ISIL to retake the city of Manbij late last month.

They have besieged the town and are advancing to the city centre under the cover of air strikes by the US-led international coalition.

ISIL has held the city since 2014, the year that the armed group seized control of large parts of Syria and neighbouring Iraq and declared its "caliphate".

Aleppo besieged

On Monday, Chris Gunness, spokesman for the United Nations agency that supports Palestinian refugees (UNRWA), said a driver who works for the agency in Syria was killed after suffering a shrapnel wound in the northern city of Aleppo.

Gunness said Yaser Mahmoud Shuaeeb, a 45-year-old father of six, died on Sunday.

Aleppo has witnessed some of the worst fighting in Syria over the past months. On Sunday, government forces besieged rebel-held neighbourhoods of the contested city.

READ MORE: Pressure mounts in Aleppo after supply line cut

Gunness said that UNRWA reported two other incidents on Sunday.

In one, a mortar shell landed 600 metres from the UN agency's office in Damascus. In the other, a missile hit close to the Nairab refugee camp south of Aleppo. The incidents caused no injuries, he said.

The death toll in the Syrian conflict, which began with mostly unarmed demonstrations against President Bashar al-Assad in March 2011, has risen to more than 280,000 people, while half the country's population have been forced from their homes, according to UN estimates.

Staffan de Mistura, UN special envoy to Syria, estimated last month that the actual death toll could be as high as 400,000 people.