BISHKEK – Police in the Central Asian state of Kyrgyzstan, a focus of Russian-U.S. rivalry, detained dozens of opposition activists Wednesday after they staged two marches in protest at last week's presidential election.

Regional powers are worried that opposition anger over the disputed July 23 vote could spill over into broader unrest in a country where Moscow and Washington both maintain air bases.

Official results gave incumbent President Kurmanbek Bakiyev 76 percent of the vote. Opposition challenger Almazbek Atambayev got 8 percent and said the election was fraudulent.

Waving flags and shouting Justice!, 50 protesters marched through the capital Bishkek but were swiftly intercepted by the police who blocked their path and snatched away their banners.

After a scuffle, police detained most of the protesters.

They (activists) broke public security rules, Gulya Kozhokulova, a district prosecutor, told reporters. Police acted in line with the law.

In a separate scuffle, police dispersed a group of activists who had gathered on the outskirts of Bishkek and started marching toward the center.

Some 20 men were detained for violating public order, Deputy Interior Minister Sabyrbek Kurmanaliyev said.

The opposition said it would stage more protests across the Muslim nation ahead of an informal summit of a Russian-dominated security bloc in Kyrgyzstan Friday, due to be attended by Russian President Dmitry Medvedev.

The ex-Soviet republic lies at the center of geopolitical competition between Russia and the United States in the vast region stretching between Afghanistan, Iran, China and Russia.

Its stability is important to efforts to contain violence in Afghanistan and prevent it spilling over into the region.

Seeking to offset U.S. policy in the region, Russia wants to set up a second military hub in Kyrgyzstan's south -- an area where the government says Islamist militants are on the rise.

Speaking outside his party headquarters in Bishkek, Atambayev told a crowd of about 100 supporters he would personally lead a march Thursday to the town of Balykchi.

Balykchi was the site of clashes on election day when police fired in the air to break up a crowd protesting against what they said was election fraud.

They are going to hand long jail terms to those who were trying to stop ballot machinations there, Atambayev said.

The opposition has also vowed to block roads in a resort in east Kyrgyzstan where the security summit is due to take place. In a move that has galvanized the opposition, the Organization for Security and Cooperation in Europe has also criticized the vote, saying its monitors witnessed widespread cases of ballot box stuffing and multiple voting.

Kyrgyzstan has rejected all criticism, saying the vote was fair. In a post-election speech Tuesday, Bakiyev promised to work hard to bring more reform and promote democracy.

(Writing by Maria Golovnina and Olzhas Auyezov)