KIEV, Ukraine (CNN) -- Opposition leader Viktor Yushchenko has said Ukraine will finally be free after declaring himself the winner of the rerun of fraud-filled presidential elections.
However, despite Western monitors declaring the election came closer to meeting international standards, supporters of the pro-Russian candidate, Prime Minister Viktor Yanukovych on Monday vowed to challenge the results in court.
Several hours earlier, with exit polls showing his lead, Yushchenko told supporters the country was witnessing the beginning of a new political era.
"After today, everything is going to change in the Ukraine," he told tens of thousands of supporters who had massed in Independence Square.
"For 14 years, we were independent, but we were not free," he said. "This is a unique, clear political victory, an elegant victory from the people who have proved their power."
"Today, the Ukrainian nation and the Ukrainian people have won. The Ukrainian people have won," he added.
Yushchenko said his job would be to determine "how to bring truth into the Ukrainian government and to make sure that freedom doesn't depend on Moscow, America or Europe. Our future depends just on ourselves."
With 96 percent of the vote counted by sunrise Monday, Yushchenko led Yanukovych 52.6 to 43.5 percent, according to the election officials.
Oleh Rybachak, Yushchenko's chief of staff, said the margin was holding up as the vote counting continued. He said according to unofficial returns for over 98 percent of the vote counted, Yushchenko's lead was still over 8.5 percent.
Yanukovych had the backing of Russian President Vladimir Putin, while Yushchenko has stronger ties to the West.
Rybachak said Yushchenko intended to go to Moscow right away for talks with Putin.
"His first trip as president will be to go to Moscow to discuss with President Putin about bilateral relations," said Rybachak. "We clearly under Russia is our priority and Yuschenko's first trip will be to Putin."
Many of the demonstrators were wearing orange, the color used by Yushchenko's campaign. They cheered and waved flags.
The bitterly contested race was a repeat of a November 21 election whose results were thrown out due to widespread fraud. Yanukovych won the official count in that election.
In response, Yushchenko supporters gathered daily in the square, calling for democratic elections.
Yushchenko's campaign officials expressed confidence the election results could not be "stolen" this time.
At polling sites Sunday, 12,000 international observers were on hand. The election was closely watched by world leaders, as it could determine Ukraine's relationship with Europe and Russia.
The International Election Observation Mission issued a statement Monday saying the election "brought Ukraine substantially closer to meeting international standards.
Throughout the election an engaged civil society demonstrated an active interest in the democratic process."
The statement said campaign conditions were "markedly more equal, observers received fewer reports of pressure on voters, the election administration was more transparent and the media more balanced than in the previous rounds."
Yushchenko's mysterious dioxin poisoning, which disfigured his face, galvanized world attention and triggered widespread speculation that someone may have tried to kill him.
The source of the poisoning has not been found, but Rybachuk said Monday a tape had surfaced indicating that former Russian secret service agents may have been involved.
"That plot was clearly with the involvement of like ex-Soviet Union experts. Many of these guys might be Russians ethnically and ex-members of the secret service," said Rybachuk.
Rybachuk also said he expected the word from international observers would be that "there was no massive fraud, nothing significant" in this round of voting.
In brief comments to reporters after the exit poll results were released, Yanukovych said he still believed he could win -- but that if he did not, he would fight as an opposition voice in parliament.
Outgoing President Leonid Kuchma has called on whoever loses to congratulate the winner the next day to help build stability. Asked whether he would call Yushchenko if the polls prove accurate, Yanukovych said he would do so, with regret.
He has argued the new election was unnecessary and unconstitutional. But international monitors condemned irregularities and fraud in last month's vote, and Ukraine's supreme court ultimately ruled the results invalid.
If Yushchenko wins, he faces the challenge of uniting the country and building stability. The country is divided geographically, with people in eastern and southern portions of the country largely supporting Yanukovych and those in other areas, including Kiev, mostly backing Yushchenko.
Amid the turmoil, many governmental institutions barely function.
Yushchenko will also face the challenge of building a relationship with Russia.
For many voters, Sunday's vote portends positive developments. Said one Yushchenko supporter, "I am very happy that our Ukrainian people rose up and fought for freedom and democracy and I think that we will have our victory."
CNN's Jill Dougherty in Kiev contributed to this report.