Ukrainian President Viktor Yanukovych's ruling Party of Regions claimed victory after the weekend balloting, in which his slate of candidates was ahead with about 30 percent of the vote with counting nearly complete.
An observer mission from the Organization for Security and Cooperation in Europe said the elections were carried out on a tilted playing field that featured "abuse of administrative resources" as well as "a lack of transparency in campaign and party financing" and unbalanced media coverage.
EU Foreign Affairs Commissioner Catherine Ashton and Stefan Fule, commissioner for EU enlargement, Tuesday issued a statement acknowledging reports of electoral abuse and warning subsequent developments in Ukraine would be monitored closely.
"We take full note of the International Observation Mission's preliminary findings on the conduct of the elections -- which present a mixed picture with several shortcomings -- and of the difficulties faced by the local electoral observers," they said.
"The final assessment will also depend on post-electoral developments, which we will watch closely," including the "tabulation of results and following up on possible electoral complaints."
The Party of Regions has come under criticism from Brussels for the jailing of former Prime Minister Yulia Tymoshenko, who is serving a 7-year prison sentence after a conviction on corruption charges and watched the elections from jail after not being allowed to run for her Fatherland Party.
Tymoshenko said she won't recognize the election results and has launched a hunger strike in protest.
OSCE observers said the absences of Tymoshenko and fellow jailed opposition figure Yuriy Lutsenko "negatively affected the election process."
That process was also unduly influenced by "powerful economic groups" who took advantage of "a lack of diversity in media ownership" and poor transparency in campaign and party financing, they said.
Ashton and Fule cited their "regret" that the prison terms, which came as the result of "trials that did not respect international standards," had prevented a fairer vote and urged Ukraine to "take further steps to reform the judiciary to avoid their recurrence."
The elections featured high turnout and were conducted peacefully, but the vote tabulation process wasn't clearly visible in many cases, the European observers said.
"Ukrainians deserved better from these elections," Andreas Gross, head of the Parliamentary Assembly of the Council of Europe delegation, said in a statement. "The 'oligarchization' of the whole process meant that citizens lost their ownership of the election, as well as their trust in it."
Ukrainian Prime Minister Mykola Azarov brushed off Western criticism and cited the findings of election observers from the Commonwealth of Independent States, the Russian-led organization of post-Soviet nations.
"To claim that the elections were undemocratic, non-transparent -- it's like black and white," the premier said Tuesday. "I met with the (CIS) observers ahead of the elections, and I said we accept and consider all absolutely objective conclusions, but we don't accept biased assessments of our elections."
Azarov noted the CIS leaders stated that, in their opinion, elections in all of Ukraine's regions were "held in an organized way, transparent and (with) high activity of voters."
Complaints were "considered promptly and substantially," he said.