The police raided the headquarters of France’s far-right National Rally party on Wednesday as part of an investigation into its campaign finances, the Paris prosecutor’s office said.

No one has been charged in the investigation, which was opened in July 2024 and aims to determine whether the nationalist, anti-immigrant party ran afoul of campaign-finance rules for France’s 2022 elections and the 2024 European elections.

The investigation was the latest in a series of allegations of financial impropriety against the party. It adds to the persistent uncertainty that has dogged French politics in recent months as parties gear up for a 2027 presidential race.

The National Rally, which has grown more powerful in recent years, has denied any wrongdoing and on Wednesday denounced the investigation as politically motivated.

“This deployment of force has only one aim: to put on a show for the news channels, to search the private correspondence of the leading opposition party, to seize all our internal documents,” Jordan Bardella, the National Rally’s president, said on X. “Nothing to do with justice, everything to do with politics.”

About 20 armed officers from France’s financial brigade took part in the raid, which was led by two investigative judges, according to Mr. Bardella.

The National Rally has, over the past decade, moved from the fringes to the heart of French politics and is now the single largest opposition party in the country’s lower house of Parliament — giving it a great deal of sway in determining the fates of prime ministers.

The party’s longtime leader, Marine Le Pen, ran unsuccessfully against President Emmanuel Macron in the past two presidential elections. Ms. Le Pen had been a front-runner for the 2027 race, but she was found guilty of embezzlement in March and was immediately barred from running for public office for five years.

She denied any wrongdoing in the case, which involved accusations that the National Rally misused several million euros in European Parliament funds between 2004 and 2016, and condemned the prosecution as politically motivated. Ms. Le Pen has appealed the verdict, and a more lenient ruling on appeal could enable her to run in 2027.

But with that outcome far from certain, the National Rally is preparing to field Mr. Bardella as its candidate in the next presidential election. Ms. Le Pen had also appealed to the European Court of Human Rights to lift the electoral ban, arguing that it violated her rights and those of her voters in the event of early legislative or presidential elections, but on Wednesday the court rejected her request.

The Paris prosecutor’s office said that Wednesday’s raid was tied to an investigation it opened after alerts from an institutional source about the party’s financing of its 2022 presidential and legislative campaigns, as well as its 2024 campaign for the European Parliament elections. It was not immediately clear what that source was.

The investigation, the prosecutor’s office said, aims to determine whether those campaigns were financed through inflated or fake invoicing for expenses — which, under French law, are partly reimbursed by the French state. Ms. Le Pen’s party was convicted in 2019 of similar offenses.

It also seeks to ascertain whether the National Rally’s recent campaigns were financed through illegal loans from private individuals to the party or its candidates. French law authorizes private loans to political parties, but under strict conditions.

Individuals can donate a maximum of 7,500 euros, or about $8,800, a year to a political party. Personal gifts to election campaigns are capped at €4,600. Parties receive significant public funding based on their electoral results.

Speaking to reporters gathered in front of the National Rally headquarters in southwestern Paris on Wednesday, party officials said the accusations of improper funding were baseless.

Laurent Jacobelli, a National Rally lawmaker and spokesman, suggested that the investigation was a pretext to sift through the party’s internal electoral strategy.

“Why the need to go see what’s happening on our computers?” he said. “Are they that afraid?”

France’s campaign-finance watchdog did not immediately respond to a request for comment. A report published last week by the watchdog found that the National Rally was the party that most relied on private loans — but it made no mention of illegal activity. In 2023, over 85 percent of private loans to political parties went to the National Rally, the report said.

The National Rally has complained for years that French banks balk at lending it money, forcing it to find different sources of financing. The party was dogged for years by suspicions that a 2014 loan from a Russian bank had left Ms. Le Pen beholden to President Vladimir V. Putin of Russia.

The National Rally is also facing an investigation at the E.U. level after a collective of news outlets reported last week that a European Parliament audit found that the party and others in a far-right group had misused at least 4.3 million euros, or about $5,000,000, in operating funds between 2019 and 2024.

The European prosecutor’s office confirmed on Wednesday that it had opened an investigation but declined to comment further. The National Rally has denied any wrongdoing.