Lebanon has also taken in more than a million refugees who fled the civil war in neighboring Syria.

The killings took place in Baakline, a town in the Chouf mountains southeast of Beirut, most of whose residents are from the Druze sect.

According to the National News Agency, the suspect first killed his wife and four Syrians. When his brother tried to stop him, the suspect killed him too. Then, while fleeing the scene, he killed two more Lebanese and one Syrian before disappearing. The security forces were still searching for him, the agency said.

The town’s mayor, Abdullah al-Ghoseini, gave a slightly different account, saying the suspect had killed three Lebanese and six Syrians, including two children, aged 10 and 15.

The killing spree lasted for about two hours and was spread over a large area, with some bodies dumped in bushes, Mr. al-Ghosseini said. He denied that the violence had been motivated by politics or revenge, suggesting that the suspect had had a “nervous breakdown.”

The suspect had been located, he said, although he was not yet under arrest.

Prime Minister Hassan Diab called the killing a “horrific crime” in a statement from his office.