U.S. Ambassador to Russia Jon Huntsman warned on Sunday that there will not be "much of a relationship left" between the U.S. and Russia if Moscow seeks to meddle in the 2018 midterm elections.

In an interview on "Fox News Sunday," Huntsman said that he had "very little doubt" that Moscow was working to interfere in the 2018 races, adding that Washington had put Russia "on notice" for the alleged efforts.

"We have an election coming up in November and if there is meddling in the election this November like we saw in 2016, we're not going to have much of a relationship left," Huntsman said.

The U.S. ambassador's comments came a day before Trump is expected to meet with Russian President Vladimir Putin in Helsinki.

The sit-down between the two leaders will be their first dedicated summit, though they have met in the past on the sidelines of other gatherings. The meeting with Putin will cap off a weeklong visit to Europe in which Trump railed against NATO allies in Brussels and criticized British Prime Minister Theresa May during a visit to London.

As he prepared to leave Washington for Europe last week, Trump predicted that his summit with Putin would be "the easiest" meeting of his trip.

Trump has repeatedly said that he wants to strengthen U.S. relations with Russia and pursue areas of mutual cooperation. But that task has been complicated by the U.S. intelligence committee's determination that Moscow meddled in the 2016 election and the ongoing special counsel probe into possible collusion between the Trump campaign and Russia.

Huntsman said on Sunday that he anticipates that Trump would raise the issue of election meddling during his meeting with Putin, saying that he suspects "it will be part of the conversation."

White House national security adviser John Bolton told ABC's "This Week" in an interview aired Sunday that the U.S. remained "quite concerned" that Russia would seek to meddle in a U.S. election again. He said the president was determined to combat those efforts.

"I think it's very clear the president's determined that we're not going to have any outsider interfere with the integrity of our electoral process," Bolton said.