Klitschko said Poroshenko “enjoys the strongest public support.” Poroshenko announced late Friday that he would stand in the presidential race.
Parliament called the early election -- scheduled for May 25 -- after voting to oust President Viktor Yanukovych in February, following three months of antigovernment protests.
Former Prime Minister Yulia Tymoshenko, who was Yanukovych's chief political rival, has also announced she plans to run again for president.
Candidates have until April 4 to register.
Ethnic Tatars from all over Crimea convened in the town of Bakhchisaray for an emergency Qurultai, or congress, to decide on the fate of the Muslim community of about 300,000 people on the Black Sea peninsula.
"There comes a moment in the life of every people when a choice must be made that will determine its future," said Tatar leader Refat Chubarov.
He urged the audience packed into a community centre to vote for a draft resolution calling for the "launch of political and legal procedures (for the) national and territorial autonomy of the Crimean Tatar people on their historical territory, Crimea."
The document notes the Crimean Tatars' concern over the recent upheaval on the peninsula, which saw pro-Russian militia and Russian troops oust Ukrainian soldiers after a Moscow-backed referendum saw the peninsula split from Ukraine.
Among more than 200 people attending the congress where Russian officials and religious leaders, including the Grand Mufti Ravil Gainutdin, also an ethnic Tatar.
Klitschko quitting the race, leaving post-revolutionary Ukraine with the Oligarch vs Oligarch choice is just tragic pic.twitter.com/mVRMNxIObY
— Maxim Eristavi (@MaximEristavi) March 29, 2014
Via Interfax:
"I can say that 'federation' is no longer a taboo word in our negotiations. I am sure we should insist on this not just because we want this but because this is a demand by the southern and eastern
regions [of Ukraine]," Lavrov said in an interview shown in an analytical program hosted by Sergei Brilyov on Rossiya-1 TV channel on Saturday
In addition, 57 percent said the United States does not have a responsibility to do something about Ukraine.
Obama himself said he could understand why people "might decide to look the other way," but that the "international order" must be protected.
So Klitchko dodges a fight with Yulia. For now, I guess. Good boxing is about strategy.
— Leonid Ragozin (@leonidragozin) March 29, 2014
Klitschko says that "the election of the President must unite the society and not become another war of all... http://t.co/PAmPHN5eKD
— MaidanOnline (@MaidanOnline) March 29, 2014
With @Vitaliy_Klychko is out of the race, @Poroshenko becomes the front-runner with 20% ahead of Tymoshenko in polls pic.twitter.com/0B17kc3WqP
— Maxim Eristavi (@MaximEristavi) March 29, 2014
#ukraine klitschko says will run for kiev mayor not for president. Against lesya orobets? Good luck with that, klitsh!
— Gulliver Cragg (@gullivercragg) March 29, 2014
.@Poroshenko at @udarKlichko congress: The 1st time in Ukraine's history top two presidential front-runners join their forces
— Maxim Eristavi (@MaximEristavi) March 29, 2014