The U.S. Department of Justice is questioning Philadelphia's use of nearly $15 million during the 2016 Democratic National Convention and what it considers overall bad bookkeeping of federal grant money.

In an audit, the department's Office of the Inspector General cited millions of dollars in what it called "unallowable and unsupported" expenses, including overtime to firefighters, meals and lodging for law enforcement agencies, and payments to vendors for items ranging from a secure bus system to credentialing for the three-day event.

The report, released Thursday, noted the city generally spent the $46 million grant for its intended purpose — keeping delegates, visitors, and residents safe during the convention. But auditors found that Philadelphia lacked proper budget management.

"We found significant deficiencies in Philadelphia's management of the grant funds, and overall, we identified over $14 million in unallowable or unsupported expenditures," Inspector General Michael Horowitz said. "We found that Philadelphia didn't have effective internal controls for grant administration."

Philadelphia officials on Friday accepted most of the findings — "we could have, and should have, done better," they said in an emailed statement — but took issue with the two largest questioned expenses: $7.6 million to partner law enforcement agencies and $6 million for contracts distributed by the convention's host committee.

They also called the July 2016 convention at the Wells Fargo Center "incredibly successful despite significant obstacles, including heat, protests, multiple major venues."

The audit is the latest inquiry into how the city and its host committee managed and paid for the event, which drew 29,000 people for Hillary Clinton's presidential nomination. Pennsylvania's auditor general last year examined $1 million the committee gave its staff in bonuses following the convention and referred the case to the IRS, given the committee's nonprofit status.

It's unclear if more fallout could come from Horowitz's review. The report lists all but one of the 13 findings as "resolved," after getting responses from the city and the Office of Justice Programs Bureau of Justice Assistance, which issued the grant. The Inspector General 's Office, however, has asked the city and bureau to provide backup documentation.

The report also noted the city's delay in providing records as the reason why the audit took more than a year to complete.

In the 61-page report, the Inspector General's Office found that the DNC host committee failed to comply with federal and local requirements when it awarded $6.4 million of the city's grant money to various vendors, including $5.2 million for a secure bus system, $146,000 for private security, and $129,000 in credentialing and scanning equipment, among other expenses.

The host committee involved the Democratic National Convention Committee in its contract decision-making, which the auditors said could create the appearance of improper political influence, because the convention committee is affiliated with the Democratic Party.

In response, the city argued that the three entities needed to coordinate "to avoid significant operational security issues." It also defended the host committee, saying it complied fully with the law and appropriately administered those funds.

The other major finding in the audit was that the city paid $7.6 million to 69 area law enforcement agencies without establishing and sharing with the agencies the federal guidelines for how the money was to be spent. The audit said that the money was to be used just on personnel, but that the city also used it to cover equipment, meals, lodging, and other items.

Auditors also criticized Philadelphia for using an average cost to calculate the $1 million in overtime costs for the Fire Department. The Inspector General's Office said the "weighted average" formula did not allow the office to determine whether the overtime charges were allowable under grant guidelines. (The city said this was due to its archaic legacy payroll system but vowed to provide actual overtime payments per firefighter.)

The audit was initiated on June 29, 2016, before the convention started.

More than 15 months later, the office was still waiting for records to justify expenses. On Oct. 3, 2017, the deadline for the 20-day notice, the city provided the federal government with several emails containing attachments, which federal officials deemed to be "incomplete" and "unreliable." It wasn't until Nov. 6, 2017, that the city turned over proper accounting records, allowing the office to conduct its audit.

The Associated Press reported that a parallel review of security grant spending at the 2016 Republican National Convention in Cleveland found only one record-keeping discrepancy, with $3.2 million worth of vehicles purchased with federal money.

Philadelphia spent $46 million of the $49 million it was awarded and has received $41 million in reimbursements.

City officials say they expect to resolve the audit findings with the Justice Department and receive the rest of the $5 million the city says it is owed in reimbursements.

City spokesperson Mike Dunn noted that the report didn't cite "any implication of fraud, waste, or abuse" and said the city would continue to cooperate with the inspectors.

"We feel confident that we can work with the Department of Justice to resolve these issues without the need for reimbursement" to the federal government, he said.