Deputy State Department spokesman Adam Ereli, spoke on Tuesday - a day before the month-long polls in the key US ally were due to wind up - about the new detention of Egyptian opposition leader Ayman Nur.
"We've also seen a number of developments over the past couple of weeks during the parliamentary elections that raise serious concerns about the path of political reform in Egypt," Ereli said.
"Clearly these actions send the wrong signal about Egypt's commitment to democracy and freedom," the spokesman said, adding that the US ambassador had taken the matter up with President Hosni Mubarak's government.
Ereli's tone contrasted sharply with that of department spokesman Sean McCormack, who complained last week of poll-related violence but called the elections "an important step on Egypt's path toward democratic reform".
But in addition to Nur's new incarceration, Ereli cited the arrest of opposition candidates and their supporters, physical abuse of election monitors and journalists, and moves to bar observers and voters from polling places.
He said Washington viewed these actions "as inconsistent with the government of Egypt's professed commitment to increase the political openness and dialogue within Egyptian society".