WASHINGTON (Reuters) - A Ku Klux Klan newspaper has declared support for Donald Trump's Republican run for U.S. president, saying America became great because it was a white, Christian republic.

The Crusader, one of the white supremacist group's most prominent publications, published a lengthy endorsement and defense of Trump's message on the front page of its current issue under the headline: "Make America Great Again."

"Make America Great Again" is Trump's campaign slogan.

The Trump campaign rejected the group's support. In a statement, campaign spokesman Steven Cheung said, "Mr. Trump and the campaign denounces hate in any form. This publication is repulsive and their views do not represent the tens of millions of Americans who are uniting behind our campaign."

The KKK is the oldest white supremacist group in the United States, tracing its roots back to the Reconstruction period in the South that followed the Civil War. In addition to anti-black views, it has expressed anti-Semitic, anti-immigrant and anti-gay views and, until recently, was anti-Roman Catholic.

Earlier this year, former KKK leader David Duke of Louisiana voiced support for Trump, saying white people are threatened in America and that he hears echoes of his views in Trump's rhetoric.

Trump drew criticism in February for failing to quickly disavow support from Duke.

Some critics have condemned as racist Trump's call for limiting Muslim immigration, building a wall along the border with Mexico and criticism of a Mexican-American judge.

In The Crusader, Pastor Thomas Robb wrote, "While Trump wants to make America great again, we have to ask ourselves, 'What made America great in the first place?'

"America was great not because of what our forefathers did -but because of who our forefathers were. America was founded as a White Christian Republic. And as a White Christian Republic it became great," Robb wrote.

Robb, based in Arkansas, heads the Knights of the Ku Klux Klan, which took over in the 1980s after the departure of Duke, according to the Southern Poverty Law Center, which tracks hates groups.

(Reporting by Mohammad Zargham; Editing by Jonathan Oatis)