"We urge Russia to cease its destabilizing activities in Ukraine and elsewhere, and its support for hostile regimes including Syria and Iran, and to instead join the community of responsible nations in our fight against common enemies and in defense of civilization itself," Trump said in Warsaw.
Just hours before the speech, Trump acknowledged that Russia may have interfered in the 2016 U.S. election but other countries may have meddled, too.
"Nobody really knows. Nobody really knows for sure," Trump said.
He has dismissed concerns about Moscow's actions as attempts to delegitimize his win.
The Warsaw speech, in which Trump also explicitly endorsed NATO's mutual defense pact, came just before Trump was set to meet with Putin for the first time as president at the G-20 summit in Germany on Friday.
Trump came into office seeking a reset of relations with Russia and hoping to cooperate in some policy areas, like fighting the terror group ISIS. However, Putin's support for ruthless Syrian President Bashar Assad, among other issues, has emerged as a hurdle to their working together.
A special counsel appointed by the Department of Justice is investigating Russian efforts to influence the election and possible ties between the Trump campaign and the Kremlin. That investigation reportedly extends to whether Trump tried to obstruct the probe.