CINCINNATI — A federal court ruled Friday that Ohio's congressional map is unconstitutional and ordered a new one be drawn for the 2020 elections.

A three-judge panel of the U.S. District Court in Cincinnati ruled unanimously that district boundaries were manipulated for partisan gain by Republican mapmakers and violates voters' rights to democratically select their representatives. The ruling blocks Ohio from holding another election under the current map.

The ruling is likely to be appealed to the U.S. Supreme Court, but the judges ordered that the state propose a new map by June 20.

Voters' rights and Democratic groups who sued Ohio Republican officials said redistricting completed after the 2010 Census yielded a statewide map that has produced an unbending 12-4 Republican advantage in Ohio's delegation. Republicans said the map was drawn with bipartisan support. They also pointed out that a new map will be drawn anyway after the 2020 Census.

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Plaintiffs said Ohioans shouldn't have to wait for a fair map.

The U.S. Supreme Court is already considering challenges to congressional maps in North Carolina, drawn by Republicans, and Maryland, drawn by Democrats.

In a case similar to Ohio's, a three-judge panel ruled this month that Michigan's congressional and legislative maps are unconstitutionally gerrymandered, and ordered the state Legislature to redraw some districts for 2020. The judges wrote that GOP mapmakers in 2011 drew maps with the goal of ensuring "durable majorities" for Republicans. An appeal is likely.

American Civil Liberties Union of Ohio Legal Director Freda Levenson had said the 10-year map was being challenged because the legal landscape has changed and because the map's results in terms of partisan representation are easily shown.

The suit called Ohio's current map "one of the most egregious gerrymanders in recent history," and that it reliably has done its job of creating a 12-to-4 advantage for Republicans in the state's congressional delegation despite the GOP having only about half the state's votes.

The longest-serving woman in U.S. House history was among plaintiffs' witnesses. Nineteen-term Rep. Marcy Kaptur, of Toledo, said her district was "hacked apart," forcing her into a Democratic primary with veteran congressman Dennis Kucinich, of Cleveland, in 2012. She won, knocking him out of Congress. Her 9th district's new map stretched eastward in a skinny line along Lake Erie all the way into Cleveland. Critics of the remap have dubbed it "the Snake by the Lake."

Attorneys for Republicans said the map resulted from compromise with Democrats and noted that each party lost one seat after reapportionment reduced Ohio's U.S. House delegation because of population shifts in the 2010 census. The delegation went from 13-5 Republican to 12-4.

"This is called democracy in action," said attorney Phil Strach. He added that both parties supported "incumbency protection" — or making it more likely an incumbent will win — because that benefits all Ohioans by giving their delegation more clout in Washington.

He said Ohioans have been voting Republican this decade, which has also seen GOP control of the both the executive and legislative branches in the state.

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Associated Press writer Julie Carr Smyth in Columbus contributed to this report.