Eds: Updates throughout

Prime Minister Viktor Yanukovych was narrowly ahead in Ukraine's presidential poll count early Monday, holding a 2.5 percentage-point margin of victory over his opponent - with most ballots counted, DPA reported.

The pro-Russia politician received 48.4 of ballots cast in the Sunday vote, while his opponent Prime Minister Yulia Tymoshenko, a populist politician, obtained 45.9 per cent of ballots cast, according to official data released by Ukraine's Central Election Committee (CEC).

Five per cent of voters marked ballots "neither candidate," with some 93 per cent of ballots counted.

The result was roughly in line with findings of seven exit polls made public after voting ended Sunday evening.

The central region of the Ukrainian capital Kiev, the scene of massive demonstrations against vote fraud in the wake of a 2004 presidential election, was relatively subdued on Monday morning.

Some 1,000 Yanukovych supporters gathered in frigid, minus 11 Celsius temperatures at a square some three kilometres from Kiev's centre to attend an outdoor rally.

The crowd was quiet, and police presence was light, with some rally participants and law enforcement officials taking cover from the cold in a nearby metro station.

Yanukovych declared victory some three hours after polls closed on Sunday evening and called on Tymoshenko to concede defeat.

"A good democrat must also be, at times, a good loser," Yanukovych said, at a Kiev press conference.

Yanukovych's victory, if confirmed, would mark an impressive come-back for the Donbass region politician, who won the 2004 vote only to have the Supreme Court cancel the result as fraudulent, after hundreds of thousands of Ukrainians led by Tymoshenko took to the streets in protest.

"I too have been defeated in my time, now it is her (Tymoshenko's) turn," he said. "Let us build our country together."

But at a Sunday evening press conference of her own, Tymoshenko said that the race was much to close to call, and she called on her supporters to await the final ballot count. Any violation of election law, or incorrect count, would be challenged in court, she said.

Tymoshenko warned that if official tallies showed evidence of substantial vote fraud committed by the Yanukovych camp, she would lead "millions" of Ukrainians in mass demonstrations.

Officials from the Organization for Security and Cooperation and Europe (OSCE), a lead agency for more than 3,300 international monitors present during the vote, were scheduled to make public a formal evaluation of the election on Monday afternoon.

Rebecca Harms, a German vote observer sent to Ukraine by the European Union, on Sunday evening told the German News Agency dpa the election seemed very well run, and fully in keeping with democratic principles.

Formal vote results are unlikely to be made public earlier than Tuesday because of the relatively small margin separating Yanukovych and Tymoshenko, CEC officials said.