President Trump said Wednesday he will seek an investigation into voter fraud that he has said allowed between three and five million people vote illegally in the November election, a claim he has yet to back up with evidence.

"I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and even, those registered to vote who are dead (and many for a long time)," Trump tweeted. "Depending on results, we will strengthen up voting procedures!"

Trump has repeatedly said that he lost the popular vote in the election to Hillary Clinton because millions of people voted illegally. However, no evidence has been presented to suggest that happened, and Trump's own lawyers argued there was no fraud in the election in a court filing challenging Green Party candidate Dr. Jill Stein's recounts.

"All available evidence shows that the 2016 election was not tainted by fraud or mistake," Trump's lawyers wrote in a Michigan filing.

Press secretary Sean Spicer was asked several times on Tuesday why Trump continues to make statements about voter fraud, despite having no evidence for his claims.

"The president does believe that. He has stated that before. I think he's stated his concerns of voter fraud and people voting illegally during the campaign," Spicer said during the briefing. "He continues to maintain that belief based on studies and evidence that people have presented to him."

Voter fraud is statistically very rare, but it's back in the headlines this week after Trump repeated his claim in a meeting with congressional leaders.

Speaker Paul Ryan said there is "no evidence" voter fraud took place in the election and other reports from the meeting state Trump didn't offer any evidence that he lost votes due to voter fraud.