Ukraine's Orange Revolution parties say they have won enough votes in tight early parliamentary elections to form a governing coalition.
A near-final tally gives the alliance of Yulia Tymoshenko and President Viktor Yushchenko a slim lead over a rival party of PM Viktor Yanukovych.
Mr Yanukovych - whose party has won the single biggest share of the vote - has also claimed victory.
Mr Yushchenko on Wednesday urged all rival camps to start coalition talks.
Mr Yanukovych welcomed the president's comments, but Ms Tymoshenko quickly ruled out any idea of sharing power with the prime minister's party.
The president had earlier demanded an urgent investigation into delays in the counting of votes in some regions.
Several parties have voiced accusations of vote-rigging, and legal challenges are expected in courts.
Europe's main election-monitoring body, the Organisation for Security and Co-operation in Europe, earlier said the elections had generally met international standards.
Just over 60% of the 37.5m eligible voters cast their ballots on Sunday, Ukraine's electoral commission said.
Results based on a count of 99.68% of the vote showed that Mr Yanukovych's Party of Regions (PR), which favours closer ties with Russia, would be the biggest in parliament with 34.31%.
The PR also has the support of the Communists, who secured 5.38% of the vote, giving the alliance a combined total of nearly 40%.
The Yulia Tymoshenko bloc (BYT) polled 30.76% of the vote, while the party of Mr Yushchenko's supporters - Our Ukraine-People's Self Defence (NUNS) - had 14.18%.
This gave the Orange allies a combined total of just nearly 45% of the vote.
The backing of the so far unaligned centrist Lytvyn bloc - which is currently holding 3.96% of the vote - could further strengthen the Orange camp.
However, Mr Yanukovych's hopes of an alliance with the Socialists have all but dashed.
Having polled only 2.86%, the party is now not expected to clear the 3% threshold required to enter the parliament.
The snap election was the third national poll in three years.
It was called in an attempt to resolve a long-running power struggle between West-leaning Mr Yushchenko and Mr Yanukovych, who is viewed as being closer to Russia.
Coalition horse-trading after last year's parliamentary elections took months and plunged Ukraine into the political turmoil which helped trigger the latest snap poll.
The EU, the US and Russia are all vying for influence in Ukraine, which straddles key Russian gas export routes to energy-hungry EU nations.
On Tuesday, Russia's gas monopoly Gazprom warned it would cut gas supplies to Ukraine unless a $1.3bn (£650m) bill is paid this month.
Previous disputes between Russia and Ukraine over gas supplies have led to cuts in gas deliveries to Europe.