Former President Jimmy Carter called President Donald Trump an illegitimate president and said Trump won the 2016 election only because of state-sponsored Russian interference.

Carter made the comments alongside his vice president, Walter Mondale, at a Friday human-rights forum hosted in Leesburg, Virginia.

"A full investigation would show that Trump didn't actually win the election in 2016," Carter said. "He lost the election and was put into office because of the Russians interfering on his behalf."

When the moderator followed up and asked whether Carter believed Trump was an illegitimate president, Carter said, "Based on what I just said, which I can't retract, yes."

Carter's comments came shortly after Trump and Russian President Vladimir Putin appeared to laugh off Russia's election interference when the two leaders met at the G20 summit in Osaka, Japan.

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Former President Jimmy Carter called President Donald Trump an illegitimate president and said Trump won the 2016 election only because of state-sponsored Russian interference to benefit him.

Carter, who is 94 years old and served from 1977 to 1981 as America's 39th president, made the comments alongside his vice president, Walter Mondale, at a Friday human-rights forum hosted in Leesburg, Virginia, and moderated by the presidential scholar Jon Meacham.

"There's no doubt that the Russians did interfere in the election," Carter said. "I think the interference, although it's not quantified, a full investigation would show that Trump didn't actually win the election in 2016. He lost the election and was put into office because of the Russians interfering on his behalf."

When Meacham followed up and asked whether Carter believed Trump was an illegitimate president, Carter said, "Based on what I just said, which I can't retract, yes."

The White House did not immediately respond to a request for comment on Carter's remarks. Carter is the first former president to describe Trump's election as illegitimate.

The redacted version of the special counsel Robert Mueller's final report, released April 18, confirmed the conclusions of every US intelligence agency that the Russian government interfered in the 2016 election to benefit the Trump campaign. The special counsel's investigation did not seek to learn whether the inference played a part in Trump's victory.

Read more: 'Don't meddle in the election': Trump appears to joke with Putin as they meet at G20 summit for the first time since Mueller report

Carter's comments came shortly after Trump and Russian President Vladimir Putin appeared to laugh off Russia's election interference when the two leaders met at the G20 summit in Osaka, Japan.

Asked by a reporter before a private meeting with Putin whether he would warn the Russian president not to interfere in the 2020 election, Trump jokingly pointed at Putin and said, "Of course I will: Don't meddle in the election," eliciting laughs and smiles from Putin and US Secretary of State Mike Pompeo.

The Mueller report identified two separate Russian interference efforts: a targeted campaign that waged cyberattacks on the Democratic National Committee and Hillary Clinton's campaign as well as an online disinformation effort spearheaded by a firm called the Internet Research Agency.

The Mueller report described in great detail how the Internet Research Agency weaponized social media to spread inflammatory content meant to be divisive, also organizing real-life protests and events.

In February 2018, the special counsel's office indicted 13 Russian nationals and three Russian companies on charges of conspiracy, conspiracy to commit wire and bank fraud, and aggravated identity theft in connection with the disinformation campaigns.

Read more: All the times figures in the Trump campaign shared false information sponsored by Russia that were included in the Mueller report

In July of that year, the special counsel's office further indicted 12 Russian security officers on charges of aggravated computer hacking, identity theft, and money laundering in connection with the hacks on the DNC and the Clinton campaign.

While the report documented extensive contacts between the Trump campaign and Russia, Mueller did not find sufficient evidence to charge Trump or anyone associated with his campaign with illegal conspiracy.

The report did say the investigation "established that the Russian government perceived it would benefit from a Trump presidency and worked to secure that outcome" and that the Trump campaign "expected it would benefit electorally from information stolen and released through Russian efforts."