At least 319 people, including dozens of women and children, were killed by the Rwanda-backed M23 rebel group that’s active in eastern Democratic Republic of Congo, according to the United Nations agency for human rights.

The killings happened in the same month that Congo and the M23 rebel group signed a so-called declaration of principles to end fighting after months of talks.

The deaths occurred over 12 days in July and are the largest documented since the group’s resurgence three years ago, UN Human Rights said in a statement on Wednesday.

“I am appalled by the attacks on civilians by the M23 and other armed groups in eastern DRC amid continued fighting, despite the ceasefire that was recently signed in Doha,” the agency’s chief Volker Türk said. Rwanda denies that it’s involved in the conflict.

Other groups have also carried out massacres, including the Allied Democratic Forces, who killed at least 40 Christian worshippers in a Sunday prayer meeting in Ituri province last month.