New York billionaire Donald Trump is firing back after reports that rival Republican presidential candidates John Kasich and Ted Cruz have formed a temporary alliance in an effort to deny Trump the delegates he needs for a first-ballot nomination at this summer's Republican National Convention in Cleveland.

"Wow, just announced that Lyin' Ted and Kasich are going to collude in order to keep me from getting the Republican nomination. DESPERATION!" Trump tweeted late Sunday

Trump added, "Lyin' Ted and Kasich are mathematically dead and totally desperate. Their donors & special interest groups are not happy with them. Sad!"

In return for Kasich ending his campaign efforts for the May 3 primary in Indiana, Cruz campaign manager Jeff Roe said the Texas senator would not challenge Kasich in Oregon and New Mexico. It marks the first time Kasich and Cruz have allied to try and block Trump’s nomination.

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Polls in Indiana show that without Kasich in the race, Cruz can defeat Trump and win most of its delegates to the national convention.

In a statement released Sunday night, John Weaver, senior strategist for Kasich’s campaign said, “Keeping Trump from winning a plurality in Indiana is critical to keeping him under 1,237 bound delegates before Cleveland.”

“In turn, we will focus our time and resources in New Mexico and Oregon, both areas that are structurally similar to the Northeast politically, where Gov. Kasich is performing well,” Weaver said.

The winner of the Indiana primary will receive 30 of the state’s 57 delegates to the national convention. The other 27 delegates will be decided by the winners of the state’s nine congressional districts.

Roe said in a statement that “having Donald Trump at the top of the ticket in November would be a sure disaster for Republicans.”

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Roe said “not only would Trump get blown out” in the general election by either former Secretary of State Hillary Clinton or Vermont Sen. Bernie Sanders, “”having him as our nominee would set the party back a generation.”

“To ensure that we nominate a Republican who can unify the Republican Party and win in November, our campaign will focus its time and resources in Indiana and in turn clear the path for Gov. Kasich to compete in Oregon and New Mexico, and we would hope that allies of both campaigns would follow our lead,” Roe said.

Both Weaver and Roe said that except for Indiana and Oregon on May 17 and New Mexico in the first week of the June, Kasich and Cruz will compete against each one another in other primary states.

The alliance is an acknowledgement of reality that neither Cruz nor Kasich can win enough delegates on their own to be nominated on the first ballot. Instead, both want to deny Trump the 1,237 delegates he needs for a first-ballot nomination and force delegates at the convention to a second ballot, where Cruz or Kasich believe they have a chance for the nomination.

– The Cox Media Group National Content Desk contributed to this report.