Al-Qaeda renegades captured another major town in northern Iraq on Sunday, forcing hundreds of families to flee into the surrounding desert as their country descended into a new round of bloodletting.

The fall of the religiously mixed town of Tal Afar to the Islamic State of Iraq and Syria (ISIS) raised the specter of deepening sectarian violence. It came as the U.S. government announced that it was drawing down staff at its embassy in Baghdad.

This is the first time since the U.S.-led invasion in 2003 that the embassy has decreased its staffing levels in response to a threat posed by violence, and the move was an indication of the level of concern that the unrest could reach even into the fortresslike Green Zone, where members of the Iraqi government also reside.

Citing the “ongoing instability and violence in certain areas,” a State Department statement said the embassy will also increase the number of security personnel deployed at the heavily guarded mission. A separate Pentagon statement said “a small number” of Defense Department personnel were being sent to augment security at the facility.

The U.S. announcement compounded the sense that there is no end in sight to the chaos that erupted a week ago when ISIS militants swept unopposed into the northern city of Mosul, then rapidly advanced to within 60 miles of Baghdad, scattering the Iraqi security forces in their wake.

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Some diplomats will be relocated to the U.S. Consulate in Basra to the south; others to the consulate in Irbil, in the northern Kurdistan region; and others to Amman, Jordan, the statement said, adding that the embassy in Baghdad will remain open.

The United States “strongly supports Iraq and its people as they face security challenges from violent extremists,” the statement said.

A plea for U.S. help

But a senior adviser to Prime Minister Nouri al-Maliki said the United States needs to do more if Iraq is to be saved. Ali al-Musawi appealed to the Obama administration to commit air support and drone strikes to the fight against the militants; “otherwise there is a danger terrorism will win,” he said.

The United States is sending assistance, “and we are thankful,” he said. “But it is not the help that we are hoping for, given the scale of the dangers Iraq is facing.”

The Obama administration has dispatched an aircraft carrier to the Persian Gulf as it decides how to respond to a crisis that threatens the stability of not only Iraq, but also the entire Middle East.

Although there have been widespread reports that Iran has dispatched members of its elite Revolutionary Guard Corps to help Iraq hold back the threat, the Maliki government prefers not to accept Iranian help because of the risk of inflaming sectarian sentiments, Musawi said.

He cited Iraq’s Strategic Framework Agreement with the United States, which spells out a range of areas of mutual interest and cooperation, as the basis on which Iraq is hoping for increased U.S. military involvement.

“We have received a lot of offers of help, but we want support through legal channels and not in a way that would provoke sensitivities,” he said, a reference to the widespread perception among Iraqis that Shiite Iran interferes in the country to advance the interests of Shiites. (Shiites are the majority in Iraq, but there are also sizable Sunni and Kurdish populations. The ISIS fighters are Sunni.)

Claims of mass killings

Fears of sectarian killings have risen amid the mass rush to arms by thousands of Shiite civilians across Baghdad and the Shiite south in recent days, after senior clerics and the government issued an appeal to civilians to volunteer to fight to reinforce the beleaguered security forces.

An ISIS claim that it had executed scores of men further underscored the risk of sectarian slaughter. The group posted gruesome photos on a Twitter account showing men in civilian clothes lying face-down, shoulder to shoulder and with their hands bound, in a ditch in Salahuddin province, as masked fighters from ISIS fired at them.

A separate tweet earlier announced that 1,700 men had been executed, but it was impossible to verify the authenticity of the photos or the claim. By Sunday afternoon, Twitter appeared to have suspended the account.

At a news conference in Baghdad, Maj. Gen. Qassim Atta, a military spokesman, said the government had reasserted control over much of Salahuddin province, and he showed a video of what he said were successful airstrikes on the town of Balad in the region. All together, 278 people have been killed by the air force in the past 24 hours, he said.

But the capture of Tal Afar, a town near the Syrian border with a large population of ethnic Turkmens, many of them Shiite, suggested that the ISIS onslaught was continuing.

Residents interviewed by telephone said a day of battles between local Shiite militias and ISIS assailants came to an end Sunday night when the Sunni militants suddenly swept into the town. Hundreds of families fled on foot because the roads were barricaded, and they were planning to spend the night in the desert nearby.

“We are in the middle of nowhere,” one man interviewed by telephone said, describing scenes of desperation as families with children prepared to camp out in the wilderness.

‘Far from normal’

In Baghdad, armed militias openly drive through the streets in pickup trucks and SUVs, in scenes reminiscent of the dark days of the civil war a decade ago, when gunmen roamed the capital. In some areas, the militias manned checkpoints, according to witnesses, underscoring the extent to which the discredited army and police are taking a back seat to the fighters.

The first workday of the Iraqi week was somewhat busier than previous days, with many people heading to their jobs and opening their shops. But traffic still was light, and the city was largely deserted by mid-afternoon.

The brittle calm of the past week was shattered by a suicide bombing that killed 14 people in a marketplace, according to state television.

Such attacks have been commonplace in Baghdad for months, but the explosion came as a reminder that the insurgents have a presence in the heart of the city even as the government seeks to rally citizens to its defense.

“Things are far from normal,” said Haider Khadem, who was asked by police to shutter his calligraphy store. He said he does not believe that the ISIS fighters will reach Baghdad, “but we know they have some gunmen inside the city, and people are afraid for their lives.”

Hauslohner reported from Irbil. Loveday Morris in Kirkuk and Jason Rezaian in Tehran contributed to this report.