A week-long delay in holding Nigeria’s presidential election, which took place on Saturday, probably hurt voter turnout, an official with the joint United States observer mission said on Monday.

“It is highly probable that such a late postponement had negative effects on voter turnout,” John Tomaszewski, of the U.S. National Democratic Institute and International Republican Institute delegation, told reporters.

“More significantly, the delay also undermined public confidence in INEC,” he said, referring to the Independent National Electoral Commission.