WASHINGTON (Reuters) - President Donald Trump said on Wednesday (Jan 25) he would seek a "major investigation" on voter fraud that will focus on those who voted in two states and illegal immigrants who voted, despite numerous studies showing that voter fraud is rare in the United States

"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). Depending on results, we will strengthen up voting procedures!" Trump said on Twitter. He did not elaborate beyond the two Twitter posts.

President Trump had repeatedly claimed that he lost the popular vote at the Nov 8 election because millions of illegal immigrants had voted. He lost the popular vote by about 2.9 million votes to Mrs Hillary Clinton but won the electoral college.

State officials in charge of the election have said they found no evidence of widespread voter fraud and there is no history of it in US elections.

House of Representatives Speaker Paul Ryan, the most senior Republican in Congress, repeated on Tuesday he had seen no evidence to support Trump's claims.

Trump has bristled at references to the popular vote results, which, combined with allegations of Russian tampering in the election on his behalf, has led to criticism that his victory was not legitimate.

The former New York businessman has never substantiated his claim of widespread voter fraud.

His announcement on Twitter follows a White House press briefing on Tuesday in which his spokesman Sean Spicer confirmed that Trump continued to believe that millions of illegal immigrants voted in the election.

Spicer did not provide any evidence to support those beliefs.

Asked if Trump would initiate an investigation if he thought there had been such a large-scale assault on a bedrock American democracy, he said none was planned.

Federal investigations of voter fraud are rare. A five-year probe initiated by the George W. Bush administration turned up no evidence of voter fraud and ended in resignations and more investigations for the Department of Justice, which enforces federal voting rights laws.

Trump's attorney general nominee, Republican Senator Jeff Sessions, has been criticised for his record on voting rights and race relations.

A voter fraud case he prosecuted as a US attorney in Alabama in 1986 helped derail his confirmation as a federal judge in 1986.

In a 2007 report titled "The Truth About Voter Fraud," by the Brennan Centre cited voter fraud incident rates between
0.00004 per cent and 0.0009 per cent.

A study by the Washington Post found 31 credible cases of impersonation fraud out of more than 1 billion votes cast in elections from 2000 to 2014. Arizona State University studies in 2012 and 2016 found similarly low rate.