(CNN) Ted Cruz and John Kasich are joining forces in a last-ditch effort to deny Donald Trump the Republican presidential nomination.

Within minutes of each other, the pair issued statements late Sunday saying they will divide their efforts in upcoming contests with Cruz focusing on Indiana and Kasich devoting his efforts to Oregon and New Mexico. The strategy -- something the two campaigns have been working on for weeks -- is aimed at blocking Trump from gaining the 1,237 delegates necessary to claim to GOP nomination this summer.

The extraordinary moves reflect the national strength Trump has shown and the inability of Republicans who oppose the New York billionaire to come together to stop him. Dividing up some of the remaining primary states by putting forward one strong alternative to Trump in each could be enough to take away delegates and curb Trump's run to the nomination.

"This is a nationwide campaign and we're making a decision where to focus our time, energy and resources," Cruz told conservative radio host Laura Ingraham on Monday . "We are now focused very, very heavily on the state of Indiana. It is significant that John Kasich is pulling out of Indiana and allowing us to go directly head to head with Donald Trump."

Kasich said Monday despite the agreement, he still wants Indiana voters to support him.

"They ought to vote for me," he said during a gaggle with reporters at a Philadelphia diner.

"I'm not campaigning in Indiana and he's not campaigning in these other states, that's all. It's not a big deal," Kasich said.

Trump is the only candidate who can realistically get a first-ballot victory -- there's no mathematical path for Cruz or Kasich to clinch the nomination heading into the convention. The billionaire is poised for a strong performance Tuesday, when Republicans in Maryland, Pennsylvania, Delaware, Connecticut and Rhode Island head to the polls

Cruz campaign manager Jeff Roe said in a statement the Texas senator will focus on the May 3 Indiana primary. He called Trump at top of the GOP ticket "a sure disaster."

He added: "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."

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Kasich's chief strategist, John Weaver, said in a separate statement: "Due to the fact that the Indiana primary is winner-take-all statewide and by congressional district, keeping Trump from winning a plurality in Indiana is critical to keeping him under 1,237 bound delegates before Cleveland. We are very comfortable with our delegate position in Indiana already, and given the current dynamics of the primary there, we will shift our campaign's resources West and give the Cruz campaign a clear path in Indiana."

Trump blasted the arrangement on Twitter.

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

Wow, just announced that Lyin' Ted and Kasich are going to collude in order to keep me from getting the Republican nomination. DESPERATION! — Donald J. Trump (@realDonaldTrump) April 25, 2016

Lyin' Ted and Kasich are mathematically dead and totally desperate. Their donors & special interest groups are not happy with them. Sad! — Donald J. Trump (@realDonaldTrump) April 25, 2016

Trump social media director Dan Scavino also blasted the deal on Twitter. "Two losing politicians-mathematically eliminated from receiving the nomination-trying something NEW! They will FAIL!" he tweeted.

Talks started after Ohio

Kasich's camp has been working for weeks to get Cruz on board with a divide-and-conquer strategy against Trump.

Initial overtures started about a week after Kasich won the Ohio primary but were initially met with silence, according to a senior Kasich official. But talks -- primarily between Weaver and Roe -- started in earnest during the following weeks, as both campaigns saw a need to work something out, even before Trump's big win in the New York primary, the source said.

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The two top strategists met to hash out the details during last week's Republican National Committee meeting in Hollywood, Florida, according to a source. In fact, even as Cruz publicly called Kasich a "spoiler" and the two campaigns were literally a few rooms apart holding private meetings to woo individual and state delegates, the advisers were negotiating their plan. The deal wasn't finalized until Sunday, when they hammered out the last of the specifics.

Sunday's move is what many in the GOP have urged on for a while -- a combined "Never Trump" strategy . Both campaigns have each sought to be the one that denies Trump a first-ballot win at the Republican convention. Each has offered their own rationales for why GOP delegates would then turn to them as the party standard-bearer.

But these strategies by Kasich and Cruz have fallen short as Trump has proved a nearly unstoppable force in the Republican primary season. Kasich has won only his home state of Ohio, more than a month ago, and is far back in the delegate chase.

Cruz has remained a steady second behind Trump, but his victories have been sporadic. His initial strategy to sweep the South with heavy support for evangelical voters fell flat. Cruz has in recent contests focused more on the delegate game, picking off support in individual congressional districts even as he lost statewide in several places.

Campaigns in trouble

The two statements were the only public comments Sunday night from the campaigns, and notably only refer to three states -- Indiana, New Mexico and Oregon. California, with its treasure trove of delegates, Nebraska and West Virginia are among the states not included.

Weaver, in a tweet , indicated the campaign still plans to compete in other states besides Oregon and New Mexico, but declined to elaborate beyond the statement.

Apologize for not returning emails/answering calls, but statements speak 4 themselves. Look forward to OR, WS, CA, NM, NJ, etc & Cleveland. — John Weaver (@JWGOP) April 25, 2016

For Kasich, this arrangement also makes financial sense. The campaign finished March with only $1.2 million in the bank, and limiting its focus to two states in cooperation with Cruz is good cover to essentially shrink its footprint to a more manageable level. The cash Kasich expected after his Ohio victory never came. A big California donor presentation swing in California a few weeks ago was received positively, according to a senior official, but with limited big bundling commitments.

As Trump continues to lead, and especially following his romp in New York last week and expected victories in northeastern states this week, tensions have been mounting, especially for Cruz. According to CNN estimates, Cruz would have to win every available delegate to reach 1,237 on the first ballot, a virtual impossibility.

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Cruz has consistently called for Kasich to move aside, touting the fact that only he and Trump have won multiple states and have a way to secure the delegates needed.

The pro-Cruz Trusted Leadership PAC has continued to hit Kasich. Friday, it announced it was planning to spend $1.6 million against Kasich in Indiana. The advertisement airing in Indiana features President Barack Obama praising the Ohio governor for expanding Medicaid, which is anathema to the GOP's conservative base. A version of the ad also aired before the New York primary.

"The primary has done the job it's supposed to do, it has narrowed the field. As we stand here today, there are two people with any plausible path whatsoever to the nomination, me and Donald Trump," Cruz said Sunday in Terre Haute, Indiana.

An audience member then shouted out, "John Kasich."

Cruz's response: "As I said, plausible path."