BISHKEK — The speaker of Kyrgyzstan's parliament has resigned under pressure from rival politicians investigating corruption and links to organized crime in the nation.

Akhmatbek Keldibekov agreed to step down Monday after late-night talks in parliament that followed a rally by hundreds of his supporters in the restive south of the country. His resignation should ease the process of forming a new coalition government.

The move to oust the speaker, a prominent member of the Ata Zhurt party popular with Kyrgyz nationalists, was the major first political challenge for newly elected President Almazbek Atambayev.

The issue threatened to reignite political battles between rival factions and trigger protests in Kyrgyzstan, a predominantly Muslim country of 5.5 million people that hosts both U.S. and Russian military air bases.

As word spread of the move to force out Keldibekov, about 1,000 of his supporters, including dozens on horseback, gathered in the center of Osh, southern Kyrgyzstan's largest city and the epicenter of ethnic violence that killed hundreds in June 2010.

A further 50 supporters from Keldibekov's home region in the Alai valley, part of the bigger Osh region, rallied briefly outside the parliament building in the capital, Bishkek.

Atambayev, the pro-business former prime minister who won the presidency in an Oct. 30 election, has vowed to stamp out the corruption that has tainted previous Kyrgyz administrations.

Anti-corruption watchdog Transparency International ranked Kyrgyzstan joint 164th of 183 countries in its 2011 Corruption Perceptions Index, level with Yemen, Guinea and Cambodia.

Keldibekov had been accused of links to organized criminal groups and of abusing his powers as parliamentary speaker. He dismissed the charges as "muck-raking," although he did admit to giving a government car registration plate to a family member.

"They are accusing me of having links to the criminal world. There is no evidence for any of the accusations against me," he said after parliament's deputy speaker, Bakyt Torobayev, read out a terse resignation letter.

Kyrgyzstan, where Islamist militancy and drug-trafficking from Afghanistan threaten stability, is attempting to entrench the first parliamentary democracy in Central Asia, a region more accustomed to authoritarian presidential rule.

The October vote allowed the first peaceful transfer of the presidency in a country where violent revolutions toppled two of the three post-Soviet leaders. Roza Otunbayeva, caretaker leader since the April 2010 revolution, did not stand for re-election.

In the first sign of trouble since the vote, the three-party coalition government that has run the country for most of the year collapsed on Dec. 2, a day after Atambayev was sworn in.

The new president has asked the Social-Democratic Party of Kyrgyzstan, a former coalition member, to form a new alliance within 15 days.

In the resignation statement, Keldibekov said he would step down on Dec. 14 "in connection with the reformation of the majority coalition and in order to preserve stability."

His Ata Zhurt party has more seats than any other and was part of an uneasy three-way alliance with the Social-Democrats and the business-oriented Respublika party.

The other two parties in parliament are Ata Meken and Ar-Namys, which campaigned on a pro-Russia platform in last year's parliamentary election.