Victor Yanukovich, the winner of Ukraine's presidential election, has urged Prime Minister Yulia Tymoshenko to acknowledge defeat, turning up the pressure even as Tymoshenko challenged the result of Sunday's presidential election.

"I officially turn to the prime minister and call on her to step down and cross to the opposition," Yanukovych said in a written statement on Wednesday.

"The country does not need another political crisis. The nation has spoken for a change in power and the prime minister should take the right decision and enter opposition."

The statement came within hours of the Central Election Commission (CEC) announcing it had completed the vote count, giving Yanukovich a 3.48 percent lead over Tymoshenko.

Yanukovich's victory in Sunday's poll likely will turn Ukraine back toward Russia.

"The priority for us is the relations with Russia, the Commonwealth of Independent States (CIS)," Yanukovych said.

"Our countries are tightly linked by economy, culture, history. Our industries complete each other. We must use these advantages in favor of our nations," he added.

Yanukovich also said Ukraine needed help "from East and West" to stabilize its economy and restructure its debt.

However, Oleksandr Turchynov, the head of Tymoshenko's campaign headquarters, has claimed that there was systematic and large-scale vote rigging in Sunday's presidential election, demanding CEC re-count ballot papers at over 900 polling stations.