Kyrgyzstan's President Almazbek Atambayev addresses a news conference in Berlin, April 1, 2015. REUTERS/Fabrizio Bensch/File Photo

BISHKEK (Reuters) - Kyrgyzstan Social Democratic party formed a new governing coalition, it said on Thursday, comprising lawmakers who a day earlier voted for constitutional reforms that opponents say are aimed at extending President Almazbek Atambayev’s rule.

Atambayev, 60, is barred by the constitution from running for a second presidential term when his mandate ends next year, and critics say the proposed reform would enable him to become a powerful prime minister instead.

Atambayev has denied having such plans.

A majority of lawmakers voted on Wednesday in favor of putting the proposal to strengthen the powers of the prime minister to a national referendum on Dec. 11.

They included members of the Kyrgyzstan and Bir Boll parties, which had now joined the coalition led by the Social Democrats, the leader of its parliamentary faction, Is Omurkulov, said.

Kyrgyzstan, an impoverished Muslim-majority former Soviet republic of 6 million people in Central Asia, has been volatile in recent years and was the scene of violent protests in 2005 and 2010 which toppled successive presidents. Atambayev took office in 2011.

The previous parliamentary coalition fell apart last month after some of its lawmakers opposed the constitutional reforms laid out by the Social Democrats, whose leader is Atambayev.