Twenty people have died in a US coalition air strike that was supposed to hit an Isis target north of the militants’ de facto caliphate of Raqqa in northern Syria, reports say.

The UK-based Syrian Observatory for Human Rights said that the strike on al-Heesha, 25 miles (45km) north of the Isis stronghold, occurred overnight on Tuesday. Local activist group Raqqa is being Silently Slaughtered put the figure at 23.

US Central Command confirmed to The Independent that its strike logs suggested an attack had been carried out in the area but more specific information was needed before authorities could “determine responsibility.”

“The Coalition takes all allegations of civilian casualties seriously and will further investigate this report,” a spokesperson added. “Extraordinary efforts are made by the Coalition to identify and strike appropriate targets in order to avoid non-combatant casualties.”

The US, UK and France have been providing air support to bolster the efforts of the Kurdish-led Syrian Democratic Forces (SDF), a coalition of Kurdish and Arab militias, which over the weekend announced the start of Operation Euphrates Wrath to encircle the city of Raqqa.

The SDF has been the most successful ground force in the fight against Isis since it declared its caliphate across Syria and Iraq in 2014, although it is distrusted by US Nato ally Turkey, which has also been involved in the fighting in Syria since August.

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The coalition’s air campaign against Isis targets in and around Raqqa has been ferocious, with dozens of strikes hitting Isis military targets and armed vehicles since Sunday Central Command said.

Tuesday’s reported casualties are the first loss of civilian life in the campaign due to US-led bombing.