Image copyright Getty Images

The US Supreme Court has ruled that North Carolina Republicans improperly used race as a factor in redrawing 2011 congressional district boundaries.

The 5-3 ruling upheld a lower court decision last year forcing legislators to draft new district maps.

Two predominantly black congressional districts are invalidated as a result.

The case was the latest in a number of lawsuits accusing Republicans of trying to limit the influence of black voters by grouping them into districts.

The ruling upheld a federal district court decision that found lawmakers had used race to carve out two of North Carolina's 13 House of Representatives districts in order to benefit the Republicans.

North Carolina ballot box battle

The targeted districts - the 1st and the 12th - are both held by Democrats. Republicans hold 10 of the state's 13 seats in the House.

State Republicans argued that they tried to increase the districts' black population in order to comply with the federal Voting Rights Act, which protects minority voters.

But Justice Elena Kagan, who wrote the ruling, said the 1st district "produced boundaries amplifying divisions between blacks and whites".

Image copyright Getty Images Image caption The two North Carolina districts in question have come before the Supreme Court before

She also said of the 12th that "race, not politics, accounted for the district's reconfiguration".

The court was unanimous in striking down the 1st district while conservatives Justice Samuel Alito, Chief Justice John Roberts and Justice Anthony Kennedy dissented on the 12th district ruling.

They argued that redrawing the 12th district map was used to help Republicans and not to discriminate against black voters.

Justice Alito also said the high court ignored an earlier precedent set in 2001 when it upheld a similar version of the same district.

"A precedent of this court should not be treated like a disposable household item - say a paper plate or a napkin - to be used once and then tossed in the trash," he wrote.

Judge Neil Gorsuch, who had not yet joined the court when the arguments were heard, did not participate in the ruling.

Democratic North Carolina Governor Roy Cooper said in a statement: "The North Carolina Republican legislature tried to rig congressional elections by drawing unconstitutional districts that discriminated against African-Americans and that's wrong."

The Supreme Court in 2015 ruled 5-4 to strike down a lower court's decision that upheld a similar Republican-backed redistricting plan in Alabama.

In a separate case in March, the justices ordered a lower court to review whether Virginia's Republican-controlled legislature tried to unlawfully diminish black voter influence through its redistricting plan.

The court threw out a decision that had upheld all 12 of Virginia's legislature districts that were challenged.