By Dan Whitcomb

June 15 (Reuters) - A New York ethics board on Thursday ordered former Mayor Bill de Blasio to pay a record $474,794 for using city funds for a security detail during his long-shot 2019 presidential campaign, finding that he violated conflict of interest laws.

The city's Conflicts of Interest Board said de Blasio had required the city to pay travel expenses for a New York Police Department security detail for him and his wife while mounting a failed run for the Democratic nomination for president between May and September 2019, while still mayor https://g.co/kgs/smdFmnt of New York.

It said it had advised de Blasio, who served eight years as New York's mayor from 2013 to 2021, against using city resources before he launched the campaign, but he disregarded that advice.

The board ruled that de Blasio should repay $319,794 spent on salaries, travel costs and overtime for the security detail for 31 campaign trips outside the state.

It fined him an additional $155,000.

"When a public servant uses city resources for private purposes, it erodes the public's trust and makes city government less efficient," the board said in its three-page written decision, which followed a lengthy investigation and hearings into the matter.

De Blasio's "conduct plainly violates this prohibition," the board wrote.

The former mayor was given 30 days to pay the full amount, which according to the board included the largest such fine it had ever imposed.

Andrew Celli, a lawyer for de Blasio, said in a written statement posted to Twitter that the former mayor had sued to overturn the board's ruling.

"In a time of unprecedented threats of political violence, the COIB's reckless and arbitrary ruling threatens the safety and security of our democratically elected public servants," Celli said.

Celli cited the Jan. 6, 2021, attack on the U.S.

Capitol as an example of threats faced by political leaders.

Three of the board's five members are appointed to six-year terms by the mayor, one by the city's comptroller and one by the public advocate. (Reporting by Dan Whitcomb; Editing by Sonali Paul)