By Mark Hosenball

WASHINGTON (Reuters) - Hackers with connections to the Russian government played a role in an effort to damage centrist French politician Emmanuel Macron's presidential campaign by hacking and leaking emails and documents ahead of the election, according to two U.S. intelligence officials.

Separately, Admiral Mike Rogers, the director of the U.S. National Security Agency, told the Senate Armed Services Committee on Tuesday that Washington became "aware of Russian activity" in the French election long before purported campaign emails were leaked two days before Sunday's vote that Macron won in a landslide.

"We gave them a heads up ... "Look, we're watching the Russians, we're seeing them penetrate some of your infrastructure'," Rogers said.

The two officials and four others familiar with intelligence agency findings acknowledged that they have not found conclusive evidence that the Kremlin ordered Russian intelligence agencies to do the hacking, or that they directed it.

But it was conducted by "entities with known ties to Russian intelligence," said one of the officials, who all spoke on the condition of anonymity.

The Russian government has repeatedly denied any involvement in hacking of the French election.

Macron campaign digital director Mounir Mahjoubi told Reuters in an interview that he had no proof that Russian government-backed hackers were behind the attacks.

"We have no precise information on who did this," he told Reuters. "I have no confirmation, no proof." He said he was speaking in a personal capacity and not officially on behalf of the campaign.

Two of the U.S. government sources and one European official said there is clear evidence that Russia targeted Macron's campaign going back at least to February. Pro-European Union Macron defeated far-right nationalist Marine Le Pen, who wanted to take France out of the EU and supports Russian policy on Ukraine.

Flashpoint, a U.S. cyber intelligence firm, said over the weekend that early indications suggested the Macron leaks were the work of a hacking group known as APT 28, or Fancy Bear, which intelligence officials and cyber experts have concluded is linked to the GRU, Russia's military intelligence agency.

That group is one of two that U.S. intelligence officials have concluded was behind the hacks of Democratic Party emails during the 2016 U.S. presidential election to undermine the campaign of candidate Hillary Clinton in favor of Republican Donald Trump, who supported a warmer relationship with Russian President Vladimir Putin.

Congressional committees are investigating the allegations and whether there was collusion between Trump's campaign and Russia. Moscow has repeatedly denied meddling.

U.S. SENATOR'S QUESTIONS ON FRANCE

On Tuesday, U.S. Senator Richard Durbin sent the Justice Department, FBI and the Office of the Director of National Intelligence a letter expressing deep concern about the events in France. He asked for a "detailed accounting of the Trump Administration's assessment of the attack on the French election and the Administration's response to this attack."

Two of the U.S. officials said Russian hackers and propagandists accelerated their efforts near the end of the campaign to help Le Pen.

"After the election came down to her and Macron, they did what they could to boost her chances, and that included hacking, as well as using the French-language versions of RT and Sputnik [two Russian government-controlled media outlets] to spread propaganda and fake news," one of the officials said.

In the final days of the French election campaign, U.S.-based, pro-Trump bloggers and Twitter activists were among the most aggressive promoters of the purported Macron data leaks, which included what appeared to be private emails along with what Macron claimed were forged offshore bank account records, other officials told Reuters.

Some of the officials said U.S. government experts are puzzled by the clumsiness of the hackers who targeted Macron, noting that the major dump of Macron-related materials came shortly before the start of a two-day black-out on media coverage of the election.

Others said the hackers may have miscalculated the effect of their efforts on French voters.

"Europeans may be more resistant to Russian meddling because they've been on the front lines and have experienced more of it since World War II," one of the U.S. officials said.

Nevertheless, two officials said, France has been what one called "ground zero" in an extensive Russian espionage campaign in western Europe that began soon after Putin, a former officer in the KGB, the Soviet intelligence service, returned to the Russian presidency five years ago.

The Russian activities accelerated sharply after the EU imposed sanctions on Russia after it seized Crimea in 2014, the officials said.

In addition to hacking and other forms of cyber espionage, the efforts include attempts by the SVR, the KGB's successor, to recruit French politicians, academics, and government and industry officials, especially in the military and intelligence services.

Russian intelligence officers in France are even more numerous and active now than they were during the Cold War, and H4, the domestic counterintelligence unit of France's General Directorate for Internal Security, or DGSI, has "ramped up" to meet the threat, two of the officials said.

"During the Cold War, the U.S. was the main threat," said one of the officials. "Now EU sanctions and NATO expansion are Putin's main concerns. At the same time, the rise of far right and nationalist parties and political figures provides an opportunity to disrupt European unity."

(Additional reporting by John Walcott and Dustin Volz in Washington and Michel Rose in Paris; Editing by Jonathan Weber and Grant McCool)