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".