Exit polls showed pro-Russian candidate Viktor Yanukovych with a narrow lead over Prime Minister Yulia Tymoshenko in Ukraine's presidential run-off election Sunday.

Ukrainian opposition leader and presidential candidate Viktor Yanukovych speaks to the media in Kiev on Sunday. (Sergei Chuzavkov/Associated Press)Yanukovych declared victory, but Tymoshenko, a leader of Orange forces, rejected the exit poll data and said the race was too close to call.

"It is too soon to draw any conclusions," she said, urging supporters to fight for every ballot.

Ukraine's Central Election Commission reported early Monday that Yanukovych was leading Tymoshenko by 51.3 per cent to 43.3 per cent with 27.4 per cent of the vote counted.

The National Election Poll exit survey predicted that after the count, Yanukovych would capture 48.5 per cent of the vote to 45.7 per cent for Tymoshenko, with other voters mostly choosing "against all."

The 2.8-percentage-point gap is only slightly larger than the NEP's margin of error of plus or minus 2.5 per cent.

The NEP poll initially showed Yanukovych with a 3.2-percentage-point lead, but later released revised figures. All other major exit polls had Yanukovych winning, some by larger margins.

The race narrowed sharply from the first round vote on Jan. 17, when Yanukovych held a 10 per cent lead.

Tymoshenko has vowed to challenge a vote she claims was rigged by in Yanukovych's favour, as it was in the 2004 elections that set off the Orange Revolution.

Tymoshenko's campaign chief Alexander Turchinov insisted Sunday there was evidence of fraud. "Intrigue still remains in place, we remain certain," he said.

But Matyas Eorsi, head of the Parliamentary Assembly of the Council of Europe's election observation mission, called the balloting "calm" and "professional" and said there was no evidence the vote had been stolen.

"We are 100 per cent sure that this election was legitimate," Eorsi said. "All the international community, and even more important the Ukrainian public, can accept this result."

A preliminary report by international monitors is expected later Monday.

The election commission projected the turnout among Ukraine's 37 million voters at about 70 per cent, 3.2 percentage points higher than the Jan. 17 first-round vote in which 18 candidates competed.