Vilnius, Lithuania (CNN) -- Secretary of State Hillary Clinton called for a "full investigation" of irregularities in Sunday's parliamentary elections in which the party of Russian Prime Minister Vladimir Putin appears to have suffered a serious setback.
"We have serious concerns about the conduct of the election," she said Tuesday as ministers gathered for a meeting of the Organization for Security and Cooperation in Europe.
The 56-member nation group, whose membership stretches from the United States to Europe, Russia and Central Asia, monitors and promotes democracy and human rights in the region and, increasingly, beyond its borders.
The group was expected to discuss a draft report by the OSCE election observer mission detailing alleged attempts to stuff ballot boxes. manipulate voter lists and harass election monitors.
As Russian Foreign Minister Sergei Lavrov looked on, Clinton told the group the United States had "serious concern about the conduct of the elections," and called for a "full investigation" of all reports of fraud and intimidation."
"The Russian people, like people everywhere, deserve the right to have their voices heard and their votes counted," Clinton said. "And that means they deserve free, fair, transparent elections and leaders who are accountable to them."
With 96% of the votes counted, Putin's United Russia party took the largest share of the vote in Sunday's elections with 49.5%, followed by 19.2% for the runner-up Communist Party, according to the Central Election Commission's website on Monday. The Fair Russia party had 13.2%, and the Liberal Democratic party had 11.7%.
But the numbers add up to a significant loss. United Russia stands to lose many of the 300 seats it currently holds in the 450-seat Duma -- Russia's parliament -- possibly shedding more than 60.
The developments came as around 100 protesters were arrested in Moscow Sunday, according to official news agency RIA Novosti, citing police. Authorities detained 70 more in St. Petersburg. Police had warned protesters earlier in the day not to hold "unsanctioned rallies" in Moscow, the Interfax news agency reported.
Opposition websites, radio stations and an election monitoring group claimed they had come under online attack.
The Golos election watchdog organization said callers reported about 1,000 elections violations on a telephone hotline, while its website was under attack.Russia's Interfax news agency reported that several other radio and newspaper websites had reported attacks.
On Monday at a conference on Afghanistan in Bonn, Clinton criticized the attack on Golos and other alleged hackings, which she called " totally contrary to what should be the protected rights of people to observe elections and participate in them and disseminate information."
The allegations came as voters cast their ballots in polls for the State Duma, the lower house of Russia's parliament.
Putin, recently tapped by his United Russia party to be its presidential candidate next year, has accused the West of trying to influence the elections.
In campaigning ahead of the vote, opponents accused the ruling party of corruption and nepotism, RIA Novosti reported.
Putin said last week that his party had earned the support of "every thoughtful, objective, serious person who wants a better lot for himself, for his children and for Russia," the news agency said.
Russia's Interior Ministry opened three criminal cases and reported hundreds of other "electoral breaches," RIA Novosti said.
Moscow police said they detained about 12 people who were distributing political leaflets -- a practice banned on election day.
Golos said there was increasing pressure at the local level to block observers from accessing polls.
"It is clear that these actions are taken by authorities to undermine the achievement of our long-term goal -- to make the elections in Russia free and fair by impartial and independent monitoring," the organization said in a statement.
In a taped interview with Russia's national TV networks in September, Medvedev criticized allegations that Russia's elections had a predetermined outcome.
"I consider such statements absolutely irresponsible, deceitful and even provocative," he said.
During her remarks to the OSCE, Clinton also spoke out against the crackdown on political opposition in Belarus, where two presidential candidates from last December's election are still in prison, and the Ukraine, where opposition leader Yulia Tymoshenko was recently jailed for seven years in what she calls a political vendetta by President Victor Yanukovych.
"When authorities fail to prosecute those who attack people for exercising their rights or exposing abuses, they subvert justice and undermine the people's confidence in their governments," Clinton said. "As the Duma elections in Russia clearly demonstrate, elections that are neither free nor fair have the same effect," Clinton said.