MBAU, Democratic Republic of Congo (Reuters) - Suspected Islamist militants killed at least 15 people overnight in eastern Congo, local officials said on Saturday, in the latest massacre since the army launched a major offensive against the rebels last month.

Democratic Republic of Congo’s army initiated its latest campaign, with support from U.N. peacekeepers, on Oct. 30 to root out fighters from the Allied Democratic Forces (ADF) from the dense forests near the Ugandan border.

As was the case during previous military operations against the ADF, its fighters have retaliated by attacking civilians, killing more than 40 since last week, according to local civil society activists.

Attacks blamed by the government on the ADF have killed hundreds of civilians since 2014.

The attacks on Friday in and around the village of Mbau were carried out with bladed weapons, local officials said. Among the eight victims in Mbau were six members of a single family.

Seven members of a Pygmy ethnic group living in the nearby forest were also killed, officials said. Their bodies were found tied up and their throats had been slit.

“The rebels are attacking civilians in order to spread confusion and panic among the population,” said Donat Kibwana, the regional administrator in the nearby city of Beni.

Mbau residents said it had taken many hours for soldiers based nearby to respond, a common complaint after attacks in the area.

Army officials were not immediately available for comment.

Researchers and rights groups say some Congolese soldiers and other rebel groups have also participated in massacres since 2014 for a variety or motives often related to competition for power in lawless zones dominated by dozens of militia groups.

Several of the previous attacks by the ADF, which was founded in Uganda in 1995, have been claimed by Islamic State, but the extent of their relationship remains unclear. The ADF is not known to have publicly pledged loyalty to Islamic State.