The candidate, Almazbek Atambaev, a former prime minister, called on the public and international organizations to reject the election as unlawful. Mr. Atambaev instructed supporters who were working as observers at polling and vote-counting stations to leave, and he demanded that a new election be organized.
“The authorities understood that they would lose an honest and free election, which is why they relied on force — relied on force against their own people!” Mr. Atambaev said in a statement.
Election officials dismissed his accusations, saying that the balloting was legitimate. Official results were not expected to be released until Friday morning.
The Russian state news agency said an exit poll showed the incumbent, Kurmanbek Bakiyev, with 67 percent of the vote, and Mr. Atambaev with 13 percent. The opposition called the exit poll false and said it planned to hold street protests against the election. The government said such actions were illegal and would be blocked.
Kyrgyzstan, a former Soviet republic in Central Asia that is host to an important American military base that supports operations in Afghanistan, has regularly faced political turmoil in recent years. It has also been the site of a tug of war between the United States and Russia over influence in Central Asia.
Kyrgyz opposition leader Almazbek Atambaev, center, spoke at a rally in Bishkek on Thursday after the closing of the presidential vote.
Mr. Bakiyev took power after the so-called Tulip Revolution of 2005, which ousted a government that was considered corrupt.
He had been expected to win a second term easily, though there was disagreement in Kyrgyzstan over why. His supporters said he had steered his poor country, which has five million people, through difficult times caused by the financial crisis and had garnered strong popularity.
The opposition has derided him as an autocrat who has persecuted opposition leaders and independent journalists. Many have been arrested, attacked and even killed over the past year.
Mr. Bakiyev has accused the opposition of airing phony charges of vote-rigging in an effort to explain away its lack of popularity. Casting his ballot on Thursday, he declared that the voting would be fair, saying that the Kyrgyz people cared about democracy.
“Each person understands that the fate of the nation, and his own future, depends on his choice,” the president said.
Officials of the Organization for Security and Cooperation in Europe were in Kyrgyzstan to monitor the election, and they said they would deliver a preliminary report on Friday.
American officials have generally refrained from criticizing the Kyrgyz government in recent months. They have focused on ensuring that the United States military can remain at the air base on the outskirts of the capital, Bishkek.
In February, Mr. Bakiyev announced that he was closing the base, apparently at the behest of Moscow. But he later reversed his decision after lobbying by the Washington, which agreed to pay more rent.
By CLIFFORD J. LEVY, Published NYT July 23, 2009