WASHINGTON - President Barack Obama's administration has ramped up its attack on restrictive voting laws and partisan redrawing of political maps that could help swing key 2012 elections to Republicans.

Attorney-General Eric Holder on Tuesday blasted efforts to keep people from the polls and vowed to throw the full weight of the Justice Department behind efforts to protect voting rights.

"We need election systems that are free from fraud, discrimination and partisan influence - and that are more, not less, accessible to the citizens of this country," Holder said in remarks prepared for delivery at the Lyndon Baines Johnson presidential library in Austin, Texas.

New rules in a dozen states, after Republicans won control of their legislatures in the 2010 mid-term elections, could make it harder for as many as five million eligible voters to participate, according to a study by New York University Law School's Brennan Centre for Justice.

The states affected, including the critical battlegrounds of Florida and Ohio, account for 171 of the 270 electoral college votes needed to win the presidency, the centre said in its October report.

Holder said the department would "carefully review" changes to voting rules and practices - including political district boundaries - in the 16 states that require "preclearance" due to their history of discrimination.

"Over the years, we've seen all sorts of attempts to gain partisan advantage by keeping people away from the polls - from literacy tests and poll taxes, to misinformation campaigns telling people that Election Day has been moved, or that only one adult per household can cast a ballot," Holder said.

"The reality is that - in jurisdictions across the country - both overt and subtle forms of discrimination remain all too common. And we don't have to look far to see recent proof."

The Justice Department is currently challenging proposed redistricting plans for both the State House and the Texas Congressional delegation because they do not adequately represent the state's growing Hispanic population.

"We intend to argue vigorously at trial that this is precisely the kind of discrimination that Section 5 (of the Voting Rights Act introduced by Johnson in 1965) was intended to block," he said.

Holder also vowed to crack down on deceptive practices and pushed for the passage of legislation set to be introduced yesterday that would establish tough criminal penalties for those who engage in fraudulent voting practices.

He cited the case of the campaign manager for former Republican governor Bob Erhlich who was convicted last week of voter fraud for approving anonymous "robocalls" that went out to more than 100000 voters in Maryland's two largest majority-black jurisdictions encouraging them to stay home because the Democratic candidate had wrapped up avictory.

Foes say requirements for voters to show government-issued photo identification, tougher voter registration rules and shorter early voting period disproportionately affect the elderly, young voters, and minorities like African-Americans who typically vote for Democrats.

Supporters say the new rules will prevent illegal immigrants from voting, or thwart attempts to cast ballots in multiple states.