French prosecutors confirmed on Wednesday that the headquarters of President Emmanuel Macron's Renaissance party had been searched in an investigation into the use of consulting firms by the government since 2017.

The National Financial Prosecutors' Office indicated that the Paris offices of US consulting giant McKinsey were also searched on Tuesday, confirming a report in Le Parisien newspaper.

The use of consultants by Macron's government came under the spotlight in March after an inquiry by the French Senate concluded that public spending on them had more than doubled from 2018-2021 during the French President's first term.

"It's normal for the judiciary to investigate freely and independently to shed all the light on this subject," a Renaissance spokesperson, Loic Signor, told AFP.

Signor said the party remained at the prosecutors' disposal "to provide all useful information on the campaigns."

McKinsey also confirmed the search of its offices, saying it was "cooperating fully with the authorities."

Two probes have been underway since October, looking into possible false election campaign accounting, as well as possible favoritism and conspiracy.

Some McKinsey consultants are known to have worked as unpaid volunteers on Macron's victorious 2017 election campaign and prosecutors are thought to be probing whether this involved a hidden campaign expense.

Prosecutors are also looking into whether McKinsey enjoyed special access and treatment when winning lucrative contracts with the government.

Total spending on consulting firms reached more than a billion euros ($1.1 billion) last year, a figure frequently cited by Macron's opponents during his successful bid for a second term last April.

The prosecutors have not publicly identified Macron or his campaign teams as the targets of the inquiry, of which the President said in November that "I'm not scared of anything."

But the use of expensive foreign firms for strategic advice - dubbed "McKinseygate" by French media - shocked many French voters even as Macron has repeatedly defended the contracts.

France has strict rules on the financing of election campaigns and political parties, which have led to many convictions in recent decades.

Former French President Nicolas Sarkozy received a one-year prison sentence in September 2021 for illegal financing of his 2012 re-election bid.