Klitschko also told members of his UDAR party that Ukraine should aim to join the European Union fully.
"We need to have a joint democratic nominee. It has to be a candidate with the highest chances of winning. Today, I believe such a candidate is Petro Poroshenko," he told a party convention in Kiev, referring to the billionaire businessman, also a former foreign minister. "Our goal is full membership of Ukraine in the EU."
Klitschko said that instead he would run for mayor of Kiev. "All reforms start in Kiev," he said.
Klitschko's withdrawal from the presidential race would set up a battle between confectionary businessman Poroshenko and Ukraine's former prime minister, Yulia Tymoshenko, in the May 25 elections.
Yulia Tymoshenko has formally joined the race to become the country's president today. "I will be the candidate of Ukrainian unity," the 53-year-old said. "The west and centre of Ukraine has always voted for me, but I was born in the east, in Dnipropetrovsk."
