BAGHDAD — Sunni militants burned homes in a mixed city northeast of Baghdad on Saturday and Sunday, forcing dozens of families to flee and raising the specter of a new intimidation tactic in Iraq's evolving civil war, Iraqi officials and witnesses said.

Militants also continued their campaign against Shiite pilgrims on Sunday, striking as the pilgrims returned home from the southern city of Karbala after observances there for the Arbaeen holiday drew millions of people over the weekend. The worst attack, a car bombing, killed at least 19 people in Baghdad as they were riding home from the south in a pickup.

Attackers burned both Sunni and Shiite homes in a neighborhood of Muqdadiya, a city of about 200,000 in Diyala Province, about 60 miles from Baghdad. There were differing reports about how many houses were affected. A security official in Diyala said that at least 30 houses were completely burned, including occupied and abandoned buildings, while a Sunni Arab politician from the area said that only six houses were destroyed. Some witnesses said as many as 100 houses were set on fire.

Victims from both sects blamed the Islamic State of Iraq, an umbrella organization for Sunni extremists that has taken over several other towns in the area. Residents said the group had recently demanded money, weapons and oaths of support from the local populace.

They said the burnings were intended to scare people into giving in or running away. Dozens of families fled the city, either left homeless by the attacks or terrified that they would be next.

"I left everything behind because I didn't want to contribute to harming other Iraqis," said Abu Muhammad Khailani, a Sunni, who said he escaped to a Shiite village for protection.

"I know why they want the money and weapons," he said. "They will kill innocent people and do whatever it takes to reach their goals."

Even before the house burnings over the weekend, Diyala had become a cauldron of daily violence, with American and Iraqi forces fighting a growing Sunni threat that has often overwhelmed the province's Shiite leaders. Residents report that in some villages, the Islamic State of Iraq brazenly flies flags that declare loyalty to Abu Omar Al-Baghdadi, the group's leader, in what appears to be both a warning and a taunt to the group's opponents.