The leaders of Ukraine's 2004 "Orange Revolution" say they will form a coalition to keep pro-Russian forces from power ahead of Sunday's parliamentary elections.
Viktor Yushchenko, the president, and Yulia Tymoshenko, the former prime minister, were in opposing political camps but are uniting to defeat current premier Viktor Yanukovych.
Viktor Yushchenko said: "I see a coalition of democratic forces as the only way forward."
Similarily, Tymoshenko said that she and Yushchenko should put aside past differences to beat Yanukovych, who favours closer ties with Moscow.
she said ahead of a rally of about 10,000 supporters in her western-Ukrainian stronghold of Lviv on Wednesday: "We should not lose time and immediately form a democratic coalition,"
Her Yulia Tymoshenko Bloc is one of three main parties contesting Sunday's poll.
Her party, Yushchenko's Our Ukraine and People's Self-Defence party, and Yanukovych's Regions party, are expected to capture most of Sunday's vote.
Power struggle
But none of the three parties is likely to win a clear majority in the Rada, or parliament, meaning coalition talks are inevitable.
If the Western-leaning Tymoshenko and Yushchenko do join up, expectations are that Tymoshenko would seek to become prime minister, forcing pro-Moscow Yanukovych out of government and into opposition.
Yanukovych has also wooed Yushchenko, saying that they could form a "broad coalition" in which he would retain the premiership.
Sunday's election was called after a power struggle between Yanukovych and Yushchenko, who wants Ukraine to join Nato and the European Union.
Tymoshenko used to serve as prime minister but was sacked after falling out with Yushchenko, her former ally in the "Orange Revolution".
Police said about 10,000 people attended Tymoshenko's demonstration, where her supporters waved the party's red love-heart flag and placards inscribed: "Yulia for prime minister".