Baghdad, Iraq ? Seeking revenge for the killing of 17 Shiite farmworkers, Shiite militiamen surged into a town north of Baghdad on Saturday to launch attacks that by nightfall killed at least 27 Sunni Arabs, many of them brought to a hospital bearing the marks of electric drills and other signs of torture, according to medical workers, residents, police and militia leaders.

Sounds of shooting suggested the killing in the city of Balad continued into the night Saturday, as reinforcements from the Shiite-controlled Interior Ministry arrived and residents cowered in their homes. “You hear nothing but gunshots,” Hasanein Ali, assistant director of Balad’s hospital, said by telephone.

In addition to the dead counted at the hospital, one Balad resident who fled the city said he had seen more bodies burned in the streets.

The fierce outbreak of violence involved Balad, a mostly Shiite city surrounded by Sunni towns, and the mostly Sunni town of Duluiya, two communities that are separated only by the Tigris River about 50 miles north of Baghdad.

On Friday, 17 Shiite laborers who had been hired to prune date palm trees in Duluiya were kidnapped, police said. The workers’ headless bodies were found outside the town later that day.

Shiite leaders in Balad said they responded to the farmworkers’ killings by asking a Baghdad office of Muqtada al-Sadr, an influential Shiite cleric, to send militiamen and weapons.

“It is necessary to take a strong stand, so that such killings will not be repeated, and so we can take our revenge,” said Taysser Musawi, a Shiite cleric in Balad.

Scores of militia fighters went to Balad in answer to the call, and residents said they targeted the city’s Sunni minority.

“The armed men, using loudspeakers, ordered Sunnis to leave the city of Balad within 24 hours or they will face death,” said Ali, the hospital official. “The city now is in the hands of the armed men and the militias.”

Ali said 27 dead Sunnis had been brought to the hospital, and said he believed more bodies had yet to be collected because of darkness and the fighting. A local Sunni resident, Muhannad Khalaf, interviewed outside Balad, said he had seen three burned bodies on the road as he fled north to safety in the Sunni city of Tikrit.

The attacks allegedly sparked fighting between townspeople of Duluiya and Balad. In Balad, police Capt. Abdul Aziz Khazrajy said the Interior Ministry in Baghdad sent security forces to the scene.

Khalaf claimed the Interior Ministry commandos had set up checkpoints and were screening travelers, seeking out Sunnis. Shiite and Sunni fighters in Iraq’s growing sectarian violence often are accused of using traffic checks to find members of the opposite sect and kill them.

A police major in Duluiya, Hussein Alwan, said by telephone that residents “are in a state of alert and top readiness. They are carrying arms, while mosques are calling on the people through loudspeakers to take up arms in defense of the town. They expect an imminent attack” by Interior Ministry commandos.