Kyrgyzstan's opposition on Saturday denounced incumbent Kurmanbek Bakiyev's landslide victory in Thursday's presidential election saying its candidate won more than 60 percent of votes and promising more protests, Reuters reported.

Both the United States and Russia have military air bases in the Central Asian country located close to Afghanistan and are closely watching the impoverished former Soviet republic for any signs of instability.

The central election commission said on Saturday that President Bakiyev had 83.8 percent of the vote after 88.3 percent of ballots had been counted. Opposition challenger Almazbek Atambayev, who has denounced the election in the ex-Soviet republic as rigged, had 7.9 percent.

"We can't stand this any more," Bakyt Beshimov, the head of Atambayev's campaign staff, told reporters. "People must fight for their rights ... We will organise further protests."

Beshimov said exit polls ordered by Atambayev's team and covering virtually all voting stations showed him winning over 60 percent of the vote with Bakiyev getting just 25 percent.

"You cannot call this an election," he said. "We don't recognize it, we demand a repeat vote."

Observers from the election monitoring arm of the Organisation for Security and Cooperation in Europe have said they were "disappointed" with the poll which failed to meet their standards.

The European Union later said it shared the OSCE's concerns. U.S.-based rights group Freedom House has also criticised what it called "the shameful conduct" of the election and urged Washington to put pressure on Kyrgyzstan over democracy.