WASHINGTON, July 1 (Reuters) - President Donald Trump lashed out on Saturday at the growing number of states refusing to give voters' names, addresses and sensitive personal information to a commission he created to investigate alleged voter fraud.

"Numerous states are refusing to give information to the very distinguished VOTER FRAUD PANEL," he wrote on Twitter. "What are they trying to hide?"

More than 20 states, including Virginia, Kentucky, California, New York and Massachusetts, have declined to provide some or all of the information, saying it was unnecessary and violated privacy.

26 PHOTOS Voter turnout at polling places across the country See Gallery Voter turnout at polling places across the country LOS ANGELES, CA - NOVEMBER 8: Horace Higgins casts his ballot at the Downtown Women's Center on Skid Row in Los Angeles, Calif., on Nov. 8, 2016. (Photo by Brian van der Brug/Los Angeles Times via Getty Images) LOS ANGELES, CA - NOVEMBER 8: Camila Chavez, 3, plays as her grandmother Alexandrian Barrios, 58, votes at a polling station set-up at Watts Towers Arts Center on November 8, 2016 in Los Angeles, California. (Photo by Irfan Khan/Los Angeles Times via Getty Images) LOS ANGELES, CA - NOVEMBER 8: Maryjane Medina, 18, a first time voter, walks up to polling booth to cast her vote at a polling station set-up at Watts Towers Arts Center on November 8, 2016 in Los Angeles, California. (Photo by Irfan Khan/Los Angeles Times via Getty Images) A man votes at a polling place at a high school in McLean, Virginia during the US presidential election on November 8, 2016. / AFP / Andrew CABALLERO-REYNOLDS (Photo credit should read ANDREW CABALLERO-REYNOLDS/AFP/Getty Images) WASHINGTON, USA - November 8: Voters fill out their ballots at a polling place in Loudon County High School during the 2016 Presidential Elections in Leesburg, Va., USA on November 8 , 2016. (Photo by Samuel Corum/Anadolu Agency/Getty Images) WASHINGTON, USA - November 8: Voters enter the polling place in Loudon County High School during the 2016 Presidential Elections in Leesburg, Va., USA on November 8 , 2016. (Photo by Samuel Corum/Anadolu Agency/Getty Images) ARLINGTON, VA - NOVEMBER 08: Voters fill out their paper ballots in a polling place on Election Day November 8, 2016 in Arlington, Virginia. Americans across the nation pick their choice for the next president of the United States. (Photo by Alex Wong/Getty Images) Voters cast their ballots during voting for the U.S presidential election in Manhasset, New York U.S., November 8, 2016. REUTERS/Shannon Stapleton NEW ALEXANDRIA, PA - NOVEMBER 8: Voters enter the Simpson Voting House, established in 1891, to vote in the presidential election on November 8, 2016 in New Alexandria, Pennsylvania. Americans across the nation make their choice for the next president of the United States today. (Photo by Jeff Swensen/Getty Images) A voter stands with a stroller outside the American Legion Post #469 polling location in Cleveland, Ohio, U.S., on Tuesday, Nov. 8, 2016. The Justice Department will deploy 500 personnel to polling stations on Election Day to help protect voters against discrimination and intimidation, down from 2012 as the result of a Supreme Court ruling that gutted part of the 1965 Voting Rights Act. Photographer: Luke Sharrett/Bloomberg via Getty Images CONCORD, NH - NOVEMBER 08: Voters fill out their ballots at the Green Street Community Center on November 8, 2016 in Concord, New Hampshire. After a contentious campaign season, Americans go to the polls today to choose the next president of the United States. (Photo by Darren McCollester/Getty Images) The early morning sun casts the shadow of a voter on a wall as he arrives at a polling location in Aliquippa, Pennsylvania, U.S., on Tuesday, Nov. 8, 2016. The Justice Department will deploy 500 personnel to polling stations on Election Day to help protect voters against discrimination and intimidation, down from 2012 as the result of a Supreme Court ruling that gutted part of the 1965 Voting Rights Act. Photographer: Pete Marovich/Bloomberg via Getty Images Democratic U.S. vice presidential candidate Senator Tim Kaine (D-VA) casts his ballot at the Hermitage Methodist Home polling station in Richmond, Virginia, U.S. November 8, 2016. REUTERS/Carlos Barria A clerk tabulates ballots at a polling station just after midnight on November 8, 2016 in Dixville Notch, New Hampshire, the first voting to take place in the 2016 US presidential election. The US presidential election got underway -- on a small scale -- as seven people in a tiny New Hampshire village cast their ballots at the stroke of midnight. Dixville Notch has had the honor of launching the voting, symbolically, since 1960. Clay Smith was the first of seven people to cast their ballots as Tuesday's long awaited Election Day began. An eighth resident voted by absentee ballot. / AFP / Alice Chiche (Photo credit should read ALICE CHICHE/AFP/Getty Images) ALEXANDRIA, VA - NOVEMBER 08: Voters wait in-line for casting their ballots outside a polling place on Election Day November 8, 2016 in Alexandria, Virginia. Americans across the nation are picking their choice for the next president of the United States. (Photo by Alex Wong/Getty Images) ALEXANDRIA, VA - NOVEMBER 08: Voters wait in-line for casting their ballots outside a polling place on Election Day November 8, 2016 in Alexandria, Virginia. Americans across the nation are picking their choice for the next president of the United States. (Photo by Alex Wong/Getty Images) A dog walks by people voting at the Brooklyn Museum polling station in the Brooklyn borough of New York City on November 8, 2016. With an anxious world watching, Americans began voting Tuesday on whether to send the first female president or a volatile populist tycoon to the White House. The kickoff marks the end to a campaign like no other -- exhausting, often bitter -- as Hillary Clinton and Donald Trump presented radically different visions of how to lead the world's greatest power. / AFP / ANGELA WEISS (Photo credit should read ANGELA WEISS/AFP/Getty Images) People arrive to a poll station to vote in Arlington, Virginia on November 8, 2016. With an anxious world watching, Americans began voting Tuesday on whether to send the first female president or a volatile populist tycoon to the White House. The kickoff marks the end to a campaign like no other -- exhausting, often bitter -- as Hillary Clinton and Donald Trump presented radically different visions of how to lead the world's greatest power. / AFP / Andrew CABALLERO-REYNOLDS (Photo credit should read ANDREW CABALLERO-REYNOLDS/AFP/Getty Images) ALEXANDRIA, VA - NOVEMBER 08: Voters wait in-line for casting their ballots outside a polling place on Election Day November 8, 2016 in Alexandria, Virginia. Americans across the nation are picking their choice for the next president of the United States. (Photo by Alex Wong/Getty Images) A voter casts his ballot in the U.S. election at Su Nueva Lavanderia in Chicago, Illinois, U.S., November 8, 2016. REUTERS/Jim Young Ballot clerks Cheryl Bourassa (L) and Judy Taylor verify the ballot count before the polls open for the 2016 U.S. presidential election in Woodstock, New Hampshire, U.S. November 8, 2016. REUTERS/Mary Schwalm Voters line up outside a polling station in Christmas, Florida on November 8, 2016. After an exhausting, wild, bitter, and sometimes sordid campaign, Americans finally began voting Tuesday for a new president: either the billionaire populist Donald Trump or Hillary Clinton, seeking to become the first woman to win the White House. / AFP / Gregg Newton (Photo credit should read GREGG NEWTON/AFP/Getty Images) Democratic presidential nominee Hillary Clinton steps away from a voting booth after voting at Douglas G. Griffin School November 8, 2016 in Chappaqua, New York. / AFP / Brendan Smialowski (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images) People voting at Congress Elementary School in the presidential election November 8, 2016 in Grand Rapids, Michigan. / AFP / JEFF KOWALSKY (Photo credit should read JEFF KOWALSKY/AFP/Getty Images) Former US President Bill Clinton (L) and Democratic presidential nominee Hillary Clinton (R)vote at Douglas G. Griffin School November 8, 2016 in Chappaqua, New York. / AFP / Brendan Smialowski (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images) MANCHESTER, NH - NOVEMBER 08: An early morning voter casts her vote at the Bishop Leo E. O'Neil Youth Center on November 8, 2016 in Manchester, New Hampshire. Voters will choose between Hillary Clinton and Donald Trump for president, as well as important races for Congress and Senate. 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"This commission was formed to try to find basis for the lie that President Trump put forward that has no foundation," Kentucky Secretary of State Alison Lundergan Grimes told Reuters previously in an interview.

The Republican president has made unsubstantiated claims that millions of people voted illegally for his Democratic rival, Hillary Clinton, in last November's election.

Trump's Presidential Advisory Commission on Election Integrity, created in May, sent a letter to 50 states asking them to turn over voter information including names, the last four digits of Social Security numbers, addresses, birth dates, political affiliations, felony convictions and voting histories.

The request from commission Vice Chairman Kris Kobach has caused a backlash from state election officials.

Indiana Secretary of State Connie Lawson said in a statement on Friday that while certain voter information is available to the public, the media, and any other person who requests the information, "the information is restricted to name, address and congressional district assignment."

Mississippi Secretary of State Delbert Hosemann had said in a statement that he did not see the letter but would rebuff the commission.

"They can go jump in the Gulf of Mexico, and Mississippi is a great state to launch from," he said.

Trump won the White House through victory in the Electoral College, which tallies wins in states, but he lost the popular vote to Clinton by some 3 million votes. He has claimed he would have won the popular vote had it not been for voter fraud.

Civil rights activists say the commission will encourage voter suppression by justifying new barriers to voting, such as requiring identity cards to vote. (Reporting by Joel Schectman, Chris Kenning and Toni Clarke; Editing by Bernard Orr and Jonathan Oatis)