Tbilisi (AFP) - Georgia's Prime Minister Irakli Garibashvili resigned on Wednesday after two years in power, with the ruling coalition struggling to boost its popularity ahead of parliamentary polls next year.

"I took the decision to leave my post," Garibashvili, head of the Georgian Dream coalition, said in a televised address to the nation, without disclosing the reason.

"All posts are temporary. Only God and the motherland are eternal," a stone-faced Garibashvili added.

Opposition politicians said that his resignation may likely be part of the coalition's efforts to reverse a rapid loss of popularity amid economic turmoil before parliamentary elections set to take place in October 2016.

"Georgian Dream is looking for a replacement for Garibashvili as its ratings are falling catastrophically," a lawmaker from opposition Free Democrats party, Irakli Chikovani, told journalists earlier on Wednesday.

"Garibashvili's resignation would be a logical step as the country is in the midst of a catastrophic economic crisis," lawmaker and one of the leaders of the opposition United National Movement party (UNM), Giga Bokeria, told journalists as rumours of the impending resignation circulated.

Garibashvili, now 33, became the youngest head of government in Europe when he was appointed to the job in the former Soviet republic in November 2013.

He was a political unknown before his billionaire tycoon predecessor Bidzina Ivanishvili named him interior minister in October 2012.

Garibashvili said Ivanishvili's resignation in 2013 "had set an example for stepping down in a timely fashion".

Media reports tipped deputy prime minister and foreign minister Giorgi Kvirikashvili as the next premier while parliament speaker David Usupashvili said "the coalition will make decision on Garibashvili’s replacement on Friday."

- 'Makes no difference' -

According to the Georgian constitution, Garibashvili's resignation leads to the dismissal of the entire cabinet which will serve on an interim basis until a new prime minister is appointed.

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President Giorgi Margvelashvili is to nominate a new prime ministerial candidate proposed by the Georgian Dream coalition within seven days.

The prime minister-designate will then nominate new cabinet members to be confirmed by the legislature.

Before taking office, Garibashvili had spent almost his entire decade-long working life in the employ of the enigmatic Ivanishvili who calls him his "beloved boy."

After years of economic boom during the reformist ex-President Mikheil Saakashvili's leadership, Georgian Dream's three years in power saw economic slowdown, rising inflation and a 44-percent devaluation of the national currency.

The coalition's approval ratings stood at just 18 percent last month, according to an opinion poll by the US-based National Democratic Institute.

Opponents had ridiculed Garibashvili's meteoric rise, criticising him for a lack of political experience and describing him as a pawn controlled by Ivanishvili from behind the scenes.

"Garibashvili is a puppet, all decisions are being made single-handedly by Ivanishvili," Bokeria said.

Ivanishvili stepped down in November 2013 to make way for Garibashvili, but was widely believed to be still calling the shots.

"Garibashvili's resignation makes no difference," Bokeria said. "The country has to get rid of Ivanishvili's informal rule."

Georgian Dream -- a motley coalition of small parties assembled by Ivanishvili -- wrested power from fervently pro-Western Mikheil Saakashvili's UNM party in the October 2012 parliamentary election.