Tens of thousands of opposition supporters rally in downtown Tbilisi, Georgia, to protest what they denounced as massive vote fraud that helped U.S.-allied Mikhail Saakashvili win a second presidential term. The protesters on Sunday demanded a runoff between Saakashvili and his chief rival.

Tbilisi, Georgia ? Tens of thousands of Georgians protested the election victory of U.S.-allied President Mikhail Saakashvili on Sunday, claiming fraud and demanding a recount.

The massive demonstration raised fears of instability in the former Soviet republic, which sits on a pipeline carrying Caspian oil to Western markets and has been battleground for influence between Russia and the United States.

It was a dramatic turnaround for Saakashvili, who rose to power as the hero of the 2003 Rose Revolution protests against fraudulent elections. He has since faced accusations of authoritarian leanings, and his popularity has fallen.

Wearing the opposition’s trademark white scarves, the protesters marched for several hours across downtown Tbilisi in freezing weather to demand a recount of the Jan. 5 election. Organizers said about 100,000 people turned out.

“Misha the Rose, you will fall soon!” protesters chanted, calling the president by his nickname.

Saakashvili won the election with 53 percent of the vote, while his main challenger, Levan Gachechiladze, had just under 26 percent, according to final official results released Sunday.

Gachechiladze and his supporters accused the government of rigging the vote and demanded that those responsible be prosecuted. They claimed Saakashvili fell far short of an outright majority and should face off against Gachechiladze in a runoff.

“Georgia doesn’t have a legitimate president,” Gachechiladze said at the demonstration. “If we stand together, we will win.”

Opposition leaders also demanded regular access to state television, which has focused on covering Saakashvili and his allies.

Observers from the Organization for Security and Cooperation in Europe gave a mixed assessment of the election, calling it “triumphant step” for democracy in Georgia while pointing to an array of violations.

Saakashvili, 40, has helped transform Georgia into a country with a growing economy and aspirations of joining the European Union and NATO, cultivating close ties with the U.S. and seeking to decrease Russia’s influence.

But a brutal police crackdown on an opposition rally in Tbilisi on Nov. 7 provoked widespread public anger and drew harsh criticism from Western governments.

Saakashvili called the early presidential vote to assuage tensions.