Illinois congressman Adam Kinzinger said Monday that Donald Trump should look into his campaign's reported ties to the Kremlin and pro-Putin figures in Ukraine.

"I think Donald Trump ought to really investigate this and where his chief adviser, what his association[s] with the Russians are," Kinzinger said.

Trump's campaign manager Paul Manafort lobbied for Ukrainian president and Putin ally Viktor Yanukovych for years, and was reportedly intended as the recipient of $12.7 million in secret cash payments from the Yanukovych government.

Kinzinger said that Manafort's name could have been "forged" on ledgers in order to "make these [cash] payouts," but noted a definite pro-Russia tilt inside the Trump campaign.

"There has been this affection in the campaign for Russia and Vladimir Putin," he said. "I have concerns for the chief adviser of Donald Trump. Having done work for a pro-Russian government in Ukraine and then, all of the sudden, there is this real affection for Russia in the campaign."

He pointed to a reported push by the Trump campaign to scale back lethal assistance to Ukrainians in the GOP platform as evidence of a sudden pro-Putin sentiment in the Republican party.

"That wasn't anything anybody was talking about, it just happened," Kinzinger said.

The shift toward Putin, he said, clashed with his Republican beliefs.

"It very much violates what I believe is a Republican which is we have to be an example to people that live behind iron curtains and under oppressive regimes of how to live life better," Kinzinger said.