Representatives from the Organization for Security and Cooperation in Europe arrived last month in Ukraine to assist with a voter-awareness campaign ahead of Sunday's parliamentary elections.
Former Polish President Aleksander Kwasniewski said if the elections are viewed as fair, the chances for broader bilateral relations with the European Union would improve for Ukraine.
"This test to have free and fair elections is decisive for the future of Ukraine," he said in a statement. "Without free and fair elections we have no chance to continue this dialogue, we have no chance to go forward."
European leaders have expressed concern about Kiev's political system following last year's conviction of former Prime Minister Yulia Tymoshenko on corruption charges. An opposition leader, Tymoshenko was accused of corruption in a 2009 deal with Russian energy company Gazprom.
Ukrainian leaders reject that allegations charges against her were politically motivated.
Members of a Polish delegation headed to observe the elections said it was premature to issue any verdict on Ukrainian political developments ahead of Election Day.