BALTIMORE (AP) — Maryland elections officials say they’ve found “significant” problems in an ongoing review of Baltimore’s primary election.

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Linda Lamone, state administrator of elections, says most of the problems were caused by untrained judges who scanned ballots that they shouldn’t have. Lamone did not know how much longer the review would take. She says workers were still finding documents on Thursday morning.

Maryland’s State Board of Elections ordered the city to rescind its certification of the April 26 primary results last week amid concerns about voting irregularities. Initially officials said they found 80 provisional ballots that hadn’t been analyzed, but Lamone says the review has now turned up 457 such ballots.

Lamone says officials haven’t seen evidence of voter fraud, but the city must reform how it runs its elections.