President Donald Trump spoke out on Monday after his former campaign chairman was indicted on 12 counts by a grand jury.

Trump said the charges against Paul Manafort referred to activity that happened "years ago," before Manafort joined the campaign.

Trump has railed against the Russia investigation in recent days.

President Donald Trump spoke out Monday morning following news that his former campaign chairman, Paul Manafort, had been indicted by a grand jury as part of special counsel Robert Mueller's investigation into Russia's interference in the 2016 election.

Manafort was indicted on 12 counts: conspiracy against the United States, conspiracy to launder money; unregistered agent of a foreign principal; false and misleading Foreign Agents Registration Act statements; false statements; and seven counts of failure to file reports of foreign bank and financial accounts.

"Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign," Trump tweeted. "But why aren't Crooked Hillary & the Dems the focus?????"

"Also, there is NO COLLUSION!" Trump concluded.

Several observers pointed out that the charges against Manafort were not related the Trump campaign and did not prove collusion between the campaign and Russia. But the former federal prosecutor Renato Mariotti noted that Monday's indictment did not mean the special counsel couldn't later bring more charges.

"He can do that — it's called 'superseding,'" Mariotti wrote.

Trump in recent days has railed against the Russia investigation, whose focus includes examining whether the Trump campaign colluded with Moscow to tilt the race in his favor. He has also repeatedly questioned why investigators aren't focusing on Hillary Clinton, his 2016 Democratic rival.

"Never seen such Republican ANGER & UNITY as I have concerning the lack of investigation on Clinton made Fake Dossier (now $12,000,000?), the Uranium to Russia deal, the 33,000 plus deleted Emails, the Comey fix and so much more," Trump said in a pair of tweets on Sunday.

Though Trump's allies have pointed at a deal from 2010 as damning evidence against Clinton, extensive reporting and fact-checking have found no signs of wrongdoing when the Obama administration allowed Rosatom, a Russian nuclear-energy firm, to acquire the Canada-based Uranium One, which had significant mining stakes in the US.

Trump went on to tweet on Sunday that instead of investigating Clinton, "they look at phony Trump/Russia 'collusion,' which doesn't exist." He continued: "The Dems are using this terrible (and bad for our country) Witch Hunt for evil politics, but the R's are now fighting back like never before."

"There is so much GUILT by Democrats/Clinton, and now the facts are pouring out," he added. "DO SOMETHING!"

Trump, as well as several of his close associates, are subjects in Mueller's investigation.