Officials and aid agencies have been warning for months that the effort to dislodge Isis from their last major stronghold could have high humanitarian cost

Eight civilians from one family, three of them children, were killed by a US airstrike on their home a few kilometres outside Mosul, relatives, officials and Kurdish troops fighting in the area say.

The attack came after a week of heavy fighting in Fadhiliya village, where Iraqi and Kurdish forces backed by coalition airpower were battling Isis militants as part of the push to recapture Iraq’s second largest city.

Pictures showed villagers uncovering bodies from a pile of rubble that had been a home. The house was hit twice, and some of the rubble and shrapnel was thrown up to 300 metres.

“We know the difference between, airstrikes, artillery and mortars, we have lived for over two years surrounded by fighting,” said Qassim a brother of one of the dead, speaking by phone from the village. Troops fighting in the area and a local MP also said the deaths were caused by an airstrike.

The Iraqi air force apparently killed more than a dozen mourners gathered at a mosque last month, but the bombing in Fadhiliya appears to be the first time a western airstrike has killed civilians since the push for Mosul began.

The US says it did conduct strikes “in the area described in the allegation” on 22 October. “The Coalition takes all allegations of civilian casualties seriously and will further investigate this report to determine the facts,” a coalition spokesperson said in an email.

The deaths are intensifying concerns about risks to ordinary Iraqis now trapped in the city. Officials and aid agencies have been warning for months that the effort to dislodge Isis from their last major stronghold in Iraq could have a high humanitarian cost, both for hundreds of thousands of civilians expected to flee the fighting, and those unable to leave areas under the militants’ control.

Isis already has added to its two year tally of atrocities in the region. Fighters have herded tens of thousands of civilians into Mosul to use as human shields, seeded whole towns with homemade bombs including many aimed at children and other non-combatants, and are summarily executing hundreds of people they fear might rise up against them.

Kurdish and Iraqi forces and their backers have pledged to protect civilians and give captured fighters their legal rights. But rights groups and NGOs say the intensity of the fight and the nature of Isis tactics, scattering militants and military installations among ordinary homes, risks a rising toll of civilian deaths from airstrikes.

“So far reported civilian fatalities have been relatively light – mainly as the battle for Mosul is focused on clearing lightly populated villages around the city. Even so, at least 20 civilians have been credibly reported killed in supporting coalition airstrikes according to our researchers,” said Chris Wood, director of the Airwars project that monitors the toll from international airstrikes in Syria and Iraq.

“As the fight pushes in towards Mosul’s suburbs, we’re concerned that the civilians trapped in the city will increasingly be at risk.”

In Fadiliya village all the dead were from one family. Qaseem, his brother Saeed and Amer who was killed, are members of a Sunni minority. They decided to endure life under the Isis harsh rule rather than face destitution in a refugee camp, and until last weekend thought they had survived.

Why is the battle for Mosul significant? Mosul is Islamic State's last urban stronghold in Iraq, and the assault is the most critical challenge yet to the group's caliphate. Since Isis leader Abu Bakr al-Baghdadi declared the establishment of a caliphate from the city in June 2014, Mosul has been central to the group’s ambitions to spread its ruthless interpretation of Islamic law throughout the Arab world and beyond. Victory over Isis appears very likely, but there are concerns about what comes next: how to provide for up to 1.3 million refugees and how to re-establish governance in a city brutalised by tyranny.

Saeed was at home, saying his prayers and hoping the battle that had raged outside was nearly over when he heard a huge blast. When a neighbour shouted over that the bomb had landed near his brother’s home, half a kilometre away at the foot of Bashiqa mountain, he raced over to find his worst fears confirmed.

“I could just see part of my nephew’s body under the rubble,” says Saeed, sobbing on the phone at the memory. “All of them were dead.” His brother and brother’s wife, their three children, a daughter-in-law and two grandchildren had all been killed. Three of the victims were children, the oldest 55 and the youngest only two years old.

“What they did to my brother’s family was unjust, he was a olive farmer and had no connection with Daesh,” Saeed said, using the Arabic acronym for Isis. Three daughters who had fled to refugee camps with their husbands and a second wife who lives in Mosul survived.

Saeed and Qassim tried to recover the bodies for burial but the fighting was so intense they had to retreat into their homes, leaving their loved ones where they had died for several days.

There were multiple airstrikes around the town at the time, as the Kurdish peshmerga tried to clear nests of fighters, including one using a minaret as a sniper post.

“We won’t take any chances” said Erkan Harki a peshmerga officer, standing on the edge of an olive grove near near the village several days after the airstrike. “We have been hit by sniper fire and mortars from inside Fadhiliya.”

This is not the first time the coalition struck civilians in Fadhiliya and a Peshmerga officer tasked with providing coordinates for air strikes said the area should be clearly marked as sensitive on maps used to plan bombing raids, because of the number of civilians.

Slaughter of Iraqi family in suspected US-led air strike hints at cost of war Read more

The airstrike was likely to be American he added, as Canadians had ended airstrikes in the area in February, and “the Americans are in charge”, he said, asking not to be named as he did not have permission to speak to media. “I can say with 95% accuracy that this strike was carried out by the Americans,” he said.

Mala Salem Shabak, the Iraqi MP who represents Fadhiliya also confirmed the deaths, and said they were caused by air strikes, as did a local administrator who asked not to be named because he still has relatives inside the village and fears Isis have not been fully routed there.

“We call on the coalition to stop bombing the villages because they are many civilians in these areas,” says Shabak, the parliamentarian when the fighting was still raging. “The bodies are under the rubble, they should be allowed to give them a dignified burial.”

On Monday Iraqi forces breached the eastern districts of Mosul as a coalition including special forces units, tribal fighters and Kurdish paramilitaries pushed ahead with its offensive.

Inhabitants of the city said that Iraqi soldiers backed by airstrikes and artillery were advancing into the eastern-most neighbourhoods, despite stiff resistance from Isis fighters.