Tens of thousands of demonstrators packed downtown Kiev on Monday to denounce alleged fraud in Ukraine's presidential runoff election, local councils in the capital and several other cities cried foul, and a major chocolate producer closed its factories in protest.

The Central Election Commission's announcement that Prime Minister Viktor Yanukovych (search) was ahead of reformist candidate Viktor Yushchenko (search) with nearly all the votes counted prompted widespread dismay among the former Soviet republic's 48 million people.

Russian President Vladimir Putin (search) sent a statement to Yanukovych to congratulate him on the result, Russian news agencies reported, but a group of international observers described Sunday's balloting as severely flawed.

Sen. Richard Lugar (search), R-Ind., chairman of the Senate Foreign Relations Committee, said outgoing President Leonid Kuchma (search) "has both the responsibility and the opportunity to review all of this and take decisive action in the best interests of the country."

Lugar did not make specific suggestions and it was not immediately clear what Kuchma and the authorities might do to defuse the sharply rising anger.

European Union officials also urged Ukrainian authorities to "urgently" review the results, saying the election had "clearly fallen short" of international standards.

As night fell in Kiev, demonstrators jammed the city's main avenue and took shelter from the subfreezing temperatures in a tent camp. Fears were high that frustrations could boil over into unrest; authorities brought busloads of special forces into the city in recent days.

Some demonstrators waved large Georgian flags, echoing the mass protests a year ago that drove President Eduard Shevardnadze (search) from office in that former Soviet republic after a fraudulent parliamentary election.

"We will not leave this place until we win," Yushchenko, wearing a scarf in his campaign color, orange, told the crowd. "The people's will cannot be broken. People's votes cannot be stolen."

As protesters milled outside the capital's city council building, its members inside passed a resolution calling on the national parliament to not recognize the election results.

Four other sizable cities — Lviv, Ternopil, Vinnytsia and Ivano-Frankivsk — announced they recognized Yushchenko as president, news agencies reported. Some 20,000 protesters rallied in Lviv, Yushchenko's western stronghold region.

The Roshen company, a major chocolate producer, announced it would close its factories for a week in protest, the Unian news agency said. If industrial protests spread, the economic growth that has been one of the struggling country's few recent points of pride could be undermined.

Yanukovych, in televised comments, called for national unity and criticized the call for public protests.

"This small group of radicals has taken upon itself the goal of splitting Ukraine," he said.

Although official results, with more than 99 percent of precincts counted, showed Yanukovych with 49.42 percent to 46.70 percent for Yushchenko, several exit polls had found Yushchenko the winner.

One poll, conducted by anonymous questionnaires under a program funded by several Western governments, including the United States, gave Yushchenko 54 percent of the vote, with Yanukovych trailing with 43 percent.

Another poll put Yushchenko ahead by 49.4 to 45.9 percent, the Interfax news agency reported.

Yanukovych spokesman Stepan Havrysh dismissed the the exit poll results as "incorrect, unscientific and even comical."

Observers working with the Organization for Security and Cooperation in Europe (search) said there were extensive indications of vote fraud, including people apparently voting multiple times and voters being forced to turn over absentee ballots to state employers.

The observers rated the voting as more flawed than the Oct. 31 first round.

"With an even heavier heart than three weeks ago, I have to repeat the message from the first round: This election did not meet a considerable number of international standards for democratic elections," said mission leader Bruce George.

"The abuse of state resources in favor of the prime minister continued, as well as an overwhelming media bias in his favor," added George.

"It is now apparent that a concerted and forceful program of election-day fraud and abuse was enacted with either the leadership or cooperation of governmental authorities," said Lugar, who came to Kiev as President Bush's envoy.

Bush warned last week that Washington would reconsider its relations with Ukraine in the event of a fraudulent election.

European Union foreign ministers called on Ukrainian authorities to "urgently" review presidential election results, arguing that the vote had "clearly fallen short" of international standards.

In contrast, the Russian head of an observer mission from former Soviet republics, Vladimir Rushailo, declared the voting "transparent, legitimate and free," according to the Interfax news agency.

Russian authorities, including Putin, had strongly praised Yanukovych during the campaign, and the nascent uprising in favor of Yushchenko is likely an embarrassment to the Kremlin as it tries to reassert influence in the ex-Soviet sphere.

The election was seen as determining whether Ukraine tilts toward the West or its traditional patron, Russia.

Yushchenko said that in addition to the tent camp in Kiev, the opposition would demand an emergency parliamentary session; reports said the session was expected Tuesday.

Yushchenko's key ally, Yulia Tymoshenko (search), called on Ukrainians to begin a general strike.

"Stop working, stop learning, make it all stop," she said.

Yushchenko foes claimed the opposition gathering in the square could try to foment civil unrest with the aim of seizing power.

"Let us negotiate quietly, let's differentiate between the truth and the dirt,and let's figure out all Yushchenko's complaints," said Vadym Konovalyuk, a lawmaker and a Yanukovych supporter.

Both camps have complained of voting problems, and throughout Sunday there were numerous media reports of scuffles at polling stations, observers being barred and journalists being detained.

One policeman guarding a polling station was found dead Sunday after apparently being hit over the head by intruders, news reports said.

Yushchenko and some of his associates went to the election commission early Monday, contending that some precincts showed improbably high turnout figures of as much as 96 percent. Some 79 percent of registered voters turned out to vote nationwide.

Yushchenko's campaign also complained that Yanukovych supporters were given absentee ballots and bused out of their native regions and back again so they could vote twice.

Yanukovych's side, meanwhile, cited voter list problems and said some stations refused to give out absentee ballots in violation of the law.

Legislators had voted to prohibit the use of absentee ballots amid fears that they could be used to falsify the results, but Kuchma refused to sign the measure Friday.

The election came after months of opposition allegations of official interference, claims Yushchenko was poisoned and a cliffhanger first-round vote riddled with complaints of intimidation.

Yushchenko says he wants to push the country to greater integration with Western Europe and has suggested seeking NATO membership.

His critics frequently portray him as an American puppet and a nationalist who would split Ukraine and alienate Russia, Ukraine's key trade partner and main energy supplier.

Yanukovych was expected to pursue close ties with Moscow; he has proposed making Russian a second official language and supports continuing Ukraine's participation in an embryonic economic union with Russia, Belarus and Kazakhstan.

Ukraine's parliament is notably contentious and capricious, with frequently shifting alliances, but Yanukovych allies are in a slight minority.

Yushchenko's foes claimed that those gathering in the square could try to foment civil unrest with the aim of seizing power.

The Central Election Commission office was guarded by riot police and armored vehicles. Several buses with Yanukovych supporters were parked nearby.

Ukraine has a large contingent of soldiers in Iraq, but both candidates support withdrawing them.