President Barack Obama warned Friday of what he called a Republican-led effort to "make it harder, not easier, for people to vote," and vowed to fight any efforts to erode the Voting Rights Act of 1965 in a speech before a civil-rights group in Manhattan.

"The right to vote is threatened today in a way that it has not been since the Voting Rights Act became law nearly five decades ago," Obama told a crowd of more than 1,600 people gathered for the National Action Network convention in Manhattan. The group is led by the Rev. Al Sharpton.

With midterm elections this fall, Obama blasted efforts in some states to curb early voting, saying "it is wrong to make anyone wait six to seven hours to vote."

He also criticized voter identification requirements being proposed in some states that he said could disenfranchise some voters -- noting not all voters have access to government-issued IDs or their birth certificates.

Republicans have long argued that identification requirements and other voting controls are reasonable measures designed to safeguard the balloting process, not to suppress voter turnout. Democrats say photo identification requirements especially affect low-income voters who may not drive and thus wouldn't have a driver's license as an official government ID.

Obama said he wasn't opposed to preventing voter fraud and ensuring identification security, but said in 12 years there have been only 10 documented cases nationwide of voter impersonation.

"Let's be clear: The voter fraud is the people who try to deny our right to vote," Obama told the crowd, which applauded throughout his speech.

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The president said U.S. Attorney General Eric Holder, who addressed the group on Wednesday, had already opened some 100 voters' rights investigations, adding "as president, I'm not going to let attacks on these rights go unchecked."

Obama said of Republicans pushing tougher requirements: "If your strategy depends on having fewer people vote, that's not a sign of strength, it's a sign of weakness."

The Republican National Committee's press office did not immediately return a request for comment.

According to a February report by the Brennan Center for Justice at New York University's School of Law, 11 states have introduced legislation making "existing photo ID laws more restrictive."

Two states have introduced measures requiring proof of citizenship, such as a birth certificate, to register or vote, and eight states have introduced legislation to limit voter registration efforts.

Public officials spotted in the crowd included Rep. Charles Rangel (D-Harlem), former Mayor David Dinkins, former Gov. David A. Paterson, Public Advocate Letitia James, Manhattan District Attorney Cy Vance and Brooklyn District Attorney Ken Thompson. Director Spike Lee also attended.