WASHINGTON (CBSNewYork/AP) -- The head of the Republican National Committee is lashing out at Donald Trump's charges that the party's presidential nomination process is "rigged.''

RNC Chairman Reince Priebus  responded to the GOP front-runner's intensifying rhetoric on Twitter late Tuesday.

Priebus says the nomination process has been known for more than a year. He says, "It's the responsibility of the campaigns to understand it. Complaints now? Give us all a break.''

Trump is going on the attack as he struggles to keep pace with rival Ted Cruz's delegate operation. Cruz made gains in Colorado, North Dakota, Louisiana and elsewhere by mastering the complicated state-by-state delegate selection process.

Trump told supporters in New York on Tuesday night that the "Republican system is absolutely rigged.''

Trump's campaign team made comments earlier this week claiming it believes Sen. Ted Cruz, R-Texas, is using "Gestapo tactics" to securedelegates in states the billionaire already won.

Speaking to NBC's "Meet the Press" on Sunday, Paul Manafort, Trump's new convention manager, said the Texas senator's campaign is "threatening" people at conventions.

"You go to these county conventions, and you see the tactics, Gestapo tactics, the scorched-earth tactics," Manafort said. "We're going to be filing several protests because reality is, you know, they are not playing by the rules."

Cruz campaign spokeswoman Catherine Frazier lashed out at the Trump camp, saying they are following the rules.

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