(AP) -- Russia can expect hard-hitting sanctions from United States lawmakers if an investigation proves that Moscow interfered in the presidential election, a U.S. senator said Wednesday during a visit to Latvia.

The Kremlin has been accused of interfering in the campaign that made Republican Donald Trump president-elect. Sen. Lindsey Graham, also a Republican, said lawmakers from both major political parties remain skeptical of the denials that have come from the government of Russian President Vladimir Putin.

"I predict there will be bi-partisan sanctions coming that will hit Russia hard, particularly Putin as an individual," Graham told reporters in Riga, the Latvian capital. He didn't elaborate on possible sanctions.

Graham said Wednesday that "Russia is trying to break the back of democracies all around the world," adding that Latvia is "constantly bombarded" with "Russian aggression and interference."

Graham is touring Estonia, Latvia and Lithuania this week with fellow Republican John McCain and Democratic Sen. Amy Klobuchar. McCain called Russia's behavior "unacceptable."

Speaking at the same event with Latvian President Raimonds Vejonis, McCain reaffirmed the U.S. commitment to the Baltics, saying the relationship with the three former Soviet states "will not change" under the new administration.

The lawmakers are due to be in Vilnius on Thursday. They also plan to visit Ukraine, Georgia and Montenegro.