The Democratic secretary of state said she had “grave concerns regarding the security and integrity” of the machines that were examined to appease ardent backers of Donald J. Trump.
Arizona’s top elections official on Thursday urged the state’s most populous county to replace hundreds of voting machines that have been examined as part of a Republican-backed review of the state’s November election.
The request added fuel to charges by impartial election observers and voting rights advocates that the review, ordered in December by the Republicans who control the State Senate, had become a political sham.
In a letter to officials of Maricopa County, which includes Phoenix, the elections official, Secretary of State Katie Hobbs, said it was unclear whether companies hired to conduct the review had sufficiently safeguarded the equipment from tampering during their review of votes.
Ms. Hobbs, a Democrat, recommended that the county replace its 385 voting machines and nine vote tabulators because “the lack of physical security and transparency means we cannot be certain who accessed the voting equipment and what might have been done to them.”
The advisory, in a letter to the county’s board of supervisors, did not contend that the machines had been breached. But Ms. Hobbs wrote that she had “grave concerns regarding the security and integrity of these machines, given that the chain of custody, a critical security tenet, has been compromised.”
She added that she had first consulted experts at the federal Cybersecurity and Infrastructure Security Agency, the national authority for election security issues.
A spokeswoman for the county elections department said county officials “will not use any of the returned tabulation equipment unless the county, state and vendor are confident that there is no malicious hardware or software installed on the devices.”
If the county decides to scrap the machines, it is unclear who would be responsible for paying to replace them. The State Senate agreed to indemnify the county against financial losses resulting from the audit.
Republicans in the State Senate who ordered the review of the election said they wanted to reassure ardent backers of former President Donald J. Trump who refused to accept his narrow loss in Arizona. The review focused on Maricopa County, which produced two-thirds of the vote statewide.
Mr. Trump has asserted that the audit would confirm his claims that his election loss was because of fraud, a charge that virtually every election expert rejects. With no formal electoral authority, the review could not change the results in Arizona.
The audit was bombarded with charges of partisan bias after the State Senate hired a firm to manage the review whose top executive had spread baseless charges that Mr. Trump’s loss in the state was a result of fraud. The criticism has only mounted after nonpartisan election observers and journalists documented repeated lapses in the review’s process for recounting ballots.