An indictment from the special counsel Robert Mueller's office alleges Russian operatives tried to hack email accounts and domains affiliated with Hillary Clinton on the same day Donald Trump called on Russia to find her "missing" emails.

"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said on July 27, 2016, the same day the indictment says hackers targeted a domain used by Clinton's personal office.

The special counsel's office on Friday brought criminal charges against 12 Russian intelligence officers suspected of hacking and meddling in the 2016 US election.

An indictment from the special counsel Robert Mueller's office on Friday alleges that Russian intelligence officers tried to hack email accounts affiliated with Hillary Clinton's campaign on the same day Donald Trump urged Russia to find emails that had been deleted from her personal accounts.

"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said at a press conference on July 27, 2016, referring to the deleted emails. "I think you will probably be rewarded mightily by our press."

Trump has said he was speaking in jest.

The indictment says Russian hackers targeted the Clinton campaign beginning in March 2016 by creating fake email accounts masking as campaign employees and sending "spearphishing" emails to real employees with links containing malware designed to give the hackers access to thousands of internal emails.

But a section of the charging document says the Russian intelligence officers, referred to as "the conspirators," stepped up their attacks to include Clinton-affiliated accounts and domains on the day Trump called on Russia to find her emails.

"For example, on or about July 27, 2016, the Conspirators attempted after hours to spearphish for the first time email accounts at a domain hosted by a third-party provider and used by Clinton's personal office," the indictment says. "At or around the same time, they also targeted seventy-six email addresses at the domain for the Clinton Campaign."

The officers are accused of using spearphishing for months to target the Democratic National Committee, the Democratic Congressional Campaign Committee, and the Clinton campaign. The indictment says July 27 was the first time they went after email accounts and domains belonging to Clinton's office.

"Yet what Trump was publicly asking the Russians to find for were Clinton's deleted *personal* emails," the Vox political correspondent Andrew Prokop tweeted on Friday. "The way this is written, including the mention of 'after hours,' definitely seems to suggest the 7/27 spearphishing attempt was in response to Trump."

The Friday indictment does not charge any American citizens or members of the Trump campaign.

The indictment's charges include two counts of conspiracy to commit an offense against the United States, eight counts of aggravated identity theft, and one count of conspiracy to launder money using cryptocurrencies, including bitcoin.