Tekebayev, 58, leads the Ata Meken (Fatherland) party's parliamentary faction and is one of the most outspoken critics of President Almazbek Atambayev, whose term ends this year. The ex-Soviet Central Asian nation will hold a presidential election on November 19. The state security service said in a statement it had detained him at an airport upon arrival from Turkey. In a separate statement, the prosecutor general's office said it suspected Tekebayev of taking a $1 million bribe from a Russian investor in 2010. Tekebayev, who was then a senior member of provisional government, promised the investor he would be able to take over a local telecommunications company, prosecutors said. Kanybek Imanaliyev, a member of parliament who belongs to Tekebayev's Ata Meken faction, said he denied any wrongdoing. 'He considers his detention... unwarranted and illegal and a continuation of political repressions,' Imanaliyev said. 'We planned to hold a party congress within a month and nominate him as candidate (for presidency).' Atambayev cannot run for re-election under the Kyrgyz constitution, but his allies in parliament successfully pushed through a referendum on a package of amendments significantly boosting the powers of the prime minister. This has prompted speculation Atambayev may either become a powerful cabinet head - although Atambayev denies having such plans - or install a loyal figure as prime minister in order to retain power in the mostly Muslim nation of 6 million.