BAGHDAD — The gunmen had surrounded the village for more than a week, refusing to let residents leave and saying they had limited time to save themselves by converting to Islam.
When that time ran out, fighters from the Islamic State stormed in, killing the men and rounding up the women and children, a survivor and Iraqi officials said Saturday.
The extent of the killings Friday in Kocho, a tiny, isolated village in northern Iraq that is home to members of the Yazidi religion, remained unclear Saturday night. Some officials said they believed that at least 80 people had died, although no one had been able to visit the site to assess the damage.
The killings were likely to heighten international concern about the plight of religious minorities in parts of northern Iraq where the Islamic State has been fighting Iraqi forces and Kurdish militias.
The spread of the Islamic State has displaced many Christians and Yazidis, and fear that Islamic State fighters would pursue the Yazidis as they fled across the barren Sinjar mountains was one reason President Barack Obama approved airstrikes on the militants.
The Islamic State seeks to create a caliphate, or government for all the world’s Muslims. It considers all who do not share its fundamentalist beliefs, including many other Sunni Muslims, infidels. That ideology has proved to be particularly destructive in Iraq, home to a range of ethnic and religious groups, including the Yazidis, a tiny religious branch that reflects some elements of Sufism and ancient regional traditions.
The killings of Yazidis on Friday came more than a week after the Islamic State surrounded the village and gave its residents a deadline to convert to Islam.
Hassan Khidr, a resident reached by telephone as he fled the area with help from an Arab neighbor, said a handful of local residents had converted in an effort to save themselves. When the village’s elders found out, they killed three of them, he said.
That news enraged the Islamic State fighters, “so they stormed the village and started killing its people,” he said.
Khidr’s hand had been wounded in the attack, and he had played dead until he was able to sneak away, he said.
The Arab man helping him flee said the Islamic State had surrounded two Yazidi villages and given them until Friday to convert to Islam. Residents of one village had fled, he said.
“But the time ran out for Kocho, so the gunmen from the Islamist State stormed it and killed their men,” said the man, who gave only his first name, Abdel-Raham, because he feared retribution by the militants.
“What is the rationale behind this mass killing?” said Hoshyar Zebari, Iraqi’s foreign minister, who said he had heard similar accounts from other survivors. “It is revenge against those they consider apostates because they have not joined their caliphate.”
It remained unclear what had become of the village’s women and children. Mr. Khidr said he did not think they had been killed, but had been rounded up and taken somewhere else.
Mahma Khalil, a Yazidi leader and a former parliament member, said he had received reports that they were taken as prisoners to the nearby town of Tal Afar.
The Islamic State has not limited its attacks to minorities. On Saturday, the Syrian Observatory for Human Rights said the group had executed more than 700 members of one tribe, most of them civilians, in the province of Deir al-Zour along the Iraqi border. The Observatory said that hundreds more people were missing and believed to be dead or detained by the Islamic State.
The Islamic State has been fighting rebel groups and armed tribes in eastern Syria, where it has seized a number of large oil fields.
In northern Iraq, airstrikes hit near the insurgent-held city of Mosul early Saturday, easing the mounting tension felt by the Kurdish forces struggling to hold the Sunni militants at bay.
Some of the strikes, which were confirmed by the U.S. Central Command, occurred near the Mosul Dam, which militants seized more than a week ago, in addition to at least one other area in the hinterland between militant and government control. Hospital officials in Mosul said the strikes had killed at least 11 Islamic State militants.
The Kurdish forces have been pushed back to operating bases on several fronts in recent weeks, including Khazir, where airstrikes occurred early Saturday along the rolling hills in front of rebel-held territory.
“This has become a front line in the battle against ISIS,” said Mohammad Mohsin Ahmedi, an assistant to Rowsch Shaways, the country’s deputy prime minister, who was visiting the area Saturday. “The airstrikes and support we have received from the international community has been very useful in our efforts to stop the ISIS advance.”
ISIS is an abbreviation of another of the Islamic State’s translated names.
It was unclear late Saturday whether U.S. or Iraqi forces had conducted the airstrikes.
Officials described the area as a crucial point along the road to Irbil, the capital of the Kurdish autonomous region in northern Iraq.
“If anyone breaks through this line, then that’s Irbil,” said Aziz Shwan Ahmed, the chief of staff in Shaways’ office. “This is defending the capital directly.”
The officials said that airstrikes had been semiregular in the past few days, and were not always a response to an imminent advance by the Sunni fighters. Kurdish fighters in the area said they did not call for the attacks Saturday morning or even see a militant push to prompt them.
“It wasn’t because they were advancing,” Mr. Ahmed said. “When the planes see ISIS movement they stop it.”