OMAHA -- Both political parties in Nebraska denounced Tuesday what they said were attempts to disenfranchise voters in Omaha.

Nebraska Democrats held a news conference Tuesday afternoon at a north Omaha polling place where a woman reported that she had received a ballot that already had been filled out for Republican presidential candidate Mitt Romney and incumbent Republican Rep. Lee Terry.

Nebraska's GOP chairman crashed the news conference to report what he described as attempts to keep Republicans from the polls.

And the campaign of Terry's Democratic challenger, John Ewing, said it had been told of a second incident in which a voter received a ballot that already had been filled out for Romney and Terry at a midtown Omaha polling place.

Nebraska Secretary of State spokeswoman Laura Strimple said the incident in north Omaha happened when one of a two-page ballot stuck in the ballot holder as it was emptied into the ballot box. The precinct worker then placed a fresh ballot into the holder to be handed to the next voter. That voter discovered the marked page, Strimple said.

Strimple said she was not aware of the second incident.

Vince Powers, incoming chairman of the Nebraska Democratic Party, said he's concerned that the reports came from Douglas County, where County Election Commissioner Dave Phipps came under fire earlier this year when weeks before the May primary, he closed dozens of polling places and nearly half the county's precincts.

Phipps said the closures were done to save money. Critics charged that the closures would make it difficult for the poorest and least mobile residents to vote. After the primary, Phipps reopened 27 polling places and added 30 precincts.

"We need to know how this occurred," Powers said of Tuesday's reports. "And frankly, the voters in Omaha ... have no confidence in Dave Phipps."

Phipps did not return messages Tuesday seeking comment.

At the news conference, Nebraska GOP Chairman Mark Fahleson said Republicans in Douglas County told the party they were receiving calls Tuesday from someone asking how they planned to vote. When the Republicans said they were voting for Romney, they were transferred to a Nebraska cellphone number that gave the voters a pre-recorded message, which said records showed they already had voted early and were ineligible to vote Tuesday.

The recording falsely claimed to be from the Nebraska GOP, Fahleson said.

"We've asked the Nebraska State Patrol to investigate," he said.