KIWANJA, Congo  At last the bullets had stopped, and François Kambere Siviri made a dash for the door. After hiding all night from firefights between rebels and a government-allied militia over this small but strategic town, he was desperate to get to the latrine a few feet away.

“Pow, pow, pow,” said his widowed mother, Ludia Kavira Nzuva, recounting how the rebels killed her 25-year-old son just outside her front door. As they abandoned his bloodied corpse, she said, one turned to her and declared, “Voilà, here is your gift.”

In little more than 24 hours, at least 150 people would be dead, most of them young men, summarily executed by the rebels last month as they tightened their grip over parts of eastern Congo, according to witnesses and human-rights investigators.

And yet, as the killings took place, a contingent of about 100 United Nations peacekeepers was less than a mile away, struggling to understand what was happening outside the gates of its base. The peacekeepers were short of equipment and men, United Nations officials said, and they were focusing on evacuating frightened aid workers and searching for a foreign journalist who had been kidnapped. Already overwhelmed, officials said, they had no intelligence capabilities or even an interpreter who could speak the necessary languages.