By Andrew Chung

WASHINGTON, Oct 21 (Reuters) - The U.S. Supreme Court on Monday threw out a challenge to Republican-drawn electoral districts in Michigan that Democrats said were illegally configured to dilute their voting power, an action taken in the aftermath of major rulings by the justices in June prohibiting federal courts from hearing such claims.

The Supreme Court's action voided an order in April by a three-judge panel to rework 34 districts in the state legislature and U.S. House of Representatives whose boundaries were crafted purely to advantage Republicans, a practice known as partisan gerrymandering.

The justices had put the panel's decision on hold before they issued their rulings in the two major gerrymandering cases from Maryland and North Carolina. In a blow to election reformers, the justices found that federal courts have no role to play in reining in electoral map manipulation by politicians aimed at entrenching one party in power.

The Supreme Court on Oct. 7 threw out a similar case from Ohio in which a lower court had invalidated 16 Republican-drawn U.S. House districts that Democrats had said were drawn to unlawfully diminish their political clout.

The June high court ruling did not foreclose partisan gerrymandering being challenged in lawsuits based on violations of a state constitution. On Sept. 3, a state court in North Carolina struck down a Republican-drawn state legislature electoral map as unlawful partisan gerrymandering under the state constitution.

In partisan gerrymandering, one political party draws legislative districts to marginalize voters who tend to support the other party. The lines are typically redrawn once a decade after the U.S. census, and in many states the party in power controls the decision-making.

Nine U.S. House and 25 state legislative districts were at issue in Michigan. A three-judge panel in Detroit on April 25 ruled in favor of Democratic voters who filed a lawsuit challenging the map, calling gerrymandering a "pernicious practice that undermines our democracy," and ordered state officials to draw new maps. (Reporting by Andrew Chung; Additional reporting by Joseph Ax; Editing by Will Dunham)