WASHINGTON (Reuters) - Republican officials on Friday defended the process for selecting delegates who will choose the party’s presidential nominee, denying a barrage of accusations from front-runner Donald Trump that it is a rigged system aimed at subverting him.Front-runner Trump has skewered the party during the past week because of rules he has lambasted as “crooked” and said the Republican National Committee “should be ashamed of themselves.” The New York billionaire moved from his preferred platforms of Twitter and television interviews to a Wall Street Journal opinion piece on Friday to air his views on the delegate-selection rules, which vary from state to state. “What we are seeing now is not a proper use of the rules, but a flagrant abuse of the rules,” Trump wrote. The RNC has stood by its process and the friction between party officials and Trump has increased all week. Without mentioning Trump by name, the party released a statement on Friday outlining the delegate selection process in states with upcoming contests - plans it said have been in place since October. “The rules surrounding the delegate selection have been clearly laid out in every state and territory and while each state is different, each process is easy to understand for those willing to learn it,” the party statement said. “It ultimately falls on the campaigns to be up to speed on these delegate rules.” RNC Chairman Reince Priebus emphasized each state writes its own rules.  “The complaining that goes on is something that I think probably distracts from what we really need to do, which is come together as Republicans,” Priebus said on NBC’s “Today” program. Trump is leading among the three Republicans seeking the party’s nomination for the Nov. 8 election to oppose either former Secretary of State Hillary Clinton or U.S. Senator Bernie Sanders on the Democratic side. The real estate mogul must win 1,237 delegates to clinch the nomination before the party’s July 18-21 convention in Cleveland. U.S. Senator Ted Cruz is trying to block Trump from reaching that number on the first round of ballot voting in hopes of triggering a contested convention. That could allow Cruz, Ohio Governor John Kasich or another last-minute entrant to win the Republican nominee. Trump has blasted such a scenario. “The political insiders have had their way for a long time,” he said in the Journal, posted online Thursday. “Let 2016 be remembered as the year the American people finally got theirs.” 