The promises had been made before, and many in the Democratic Republic of Congo expected them to be broken again: President Joseph Kabila would step down at last, and there would be a free election to choose a new leader. But on Thursday, the electoral commission postponed the vote for a week.

Three days before the long-anticipated election set for Sunday, the commission told presidential candidates that it was “technically incapable” of holding the vote that would have seen Mr. Kabila leave office after almost 18 years in power.

Time and again, the commission has delayed the election. This time, it blamed violence, technical problems — including a mysterious fire that incinerated thousands of voting machines last week — and an Ebola epidemic ravaging parts of eastern Congo.

The election was supposed to be held in 2016. But it was postponed until this year, when Mr. Kabila appeared to bend to international and regional pressure as well as street protests led by the Roman Catholic Church, one of the few institutions in the country that enjoys widespread legitimacy.