WASHINGTON (AP) — President Donald Trump said Monday that Russian President Vladimir Putin privately made an "incredible offer" to help American investigators in their prosecution of 12 Russian intelligence officers accused of hacking crimes during the 2016 presidential election.

"He offered to have the people working on the case come and work with their investigators with respect to the 12 people," Trump told reporters during a news conference in Helsinki following his joint summit with Putin. "I think that's an incredible offer, OK?"

The special counsel investigating potential coordination between the Trump campaign and the Kremlin on Friday charged a dozen Russian military intelligence officers with hacking the Democratic National Committee and the Hillary Clinton campaign and then releasing the stolen communications online as part of a sweeping conspiracy to meddle in the election.

Putin noted that Russia would expect the U.S. to return the favor and cooperate in the Russian probe against William Browder, a British investor charged in financial crimes in Russia. Browder was a driving force behind a U.S. law targeting Russian officials over human rights abuses.

It was not clear from Trump's statement what sort of help Putin was offering. The United States does not have an extradition treaty with Russia, making it uncertain that the indicted Russian officers — who are not currently in custody — will ever be prosecuted in an American courtroom.

And the detailed allegations in the 29-page indictment make clear that the FBI and Mueller's team believe they were able, through their own investigation, to pinpoint the hackers by name and establish how the cyberattacks unfolded.

Putin has long insisted that the Kremlin had nothing to do with the hacking, and Trump said the Russian leader repeated his denials during their private meeting Monday. U.S. intelligence officials have said they're confident that the Kremlin was behind the effort to help Trump defeat Clinton, and Mueller's indictment alleged that the culprits are part of a Russian military intelligence agency known as the GRU.

"So I have great confidence in my intelligence people, but I will tell you that President Putin was extremely strong and powerful in his denial today," Trump said.

Spokespeople for the Justice Department and special counsel Robert Mueller declined to comment on Trump's comments or on Putin's purported offers for assistance.

Despite Trump's assertion that Putin has offered a hand, Mueller's office has suggested that the Kremlin has been less than forthcoming in another criminal case brought against Russia.

Prosecutors in February charged 13 Russians with participating in a social media effort to sway public opinion during the election by concocting bogus Facebook ads in the names of Americans.

Mueller's office has tried to serve summonses on the defendants demanding that they appear in court, but prosecutors say the Office of the Prosecutor General of Russia declined to accept the summonses. The U.S. government also sought Russian government effort through a mutual legal assistance treaty, but according to a court filing this month, "no further steps have been taken within Russia to effectuate service."