Georgia on Wednesday plunged into political crisis after its youthful prime minister sacked his hugely popular defence minister and the foreign minister resigned in protest.

In the ensuing political turmoil in the pro-Western Caucasus nation, Irakli Alasania -- who was fired in a surprise move on Tuesday -- said his Free Democrats party was leaving the ruling coalition, robbing Prime Minister Irakli Garibashvili, 32, of a parliamentary majority.

"Free Democrats will no longer be in the coalition," the photogenic ex-defence minister, 40, told reporters.

The ruling Georgian Dream coalition was left with only 73 seats in the 150-member legislature after Free Democrats' 10-member-strong parliamentary faction quit.

Observers said the row had all the trappings of a bitter power struggle in which Garibashvili got rid of his charismatic, influential opponent.

"Internal infighting between the Georgian Dream leaders is a primary cause for the crisis. Alasania has become too popular," independent political analyst Gia Nodia told AFP.

"Foreign policy disagreements between Garibashvili and strongly pro-Western Alasania are a secondary factor."

Opinion polls have repeatedly shown that Alasania is the most popular politician in the ruling coalition.

Garibashvili sacked Alasania after a raft of corruption charges were brought against high-ranking defence ministry officials.

He nominated his little-known 36-year-old national security advisor, Mindia Janelidze, as his new defence minister.

Alasania shot back by saying the charges were "groundless and politically motivated" and levelled mainly because of his faction's support for closer ties with the West.

Alasania had been pushing for the former Soviet state to join NATO and the EU.

"We are dealing with a deliberate attack against the defence ministry, which is a direct link in our country's chain with NATO and the European Union," he told a news conference.

Garibashvili dismissed the counter-allegations as "irresponsible speculation," saying Georgia's pro-Western orientation was "irreversible".

"Georgia's membership in NATO and the European Union is the choice of our people," he said.

The future of the ruling coalition remains unclear for now.

At least 76 votes are required for a cabinet to win a confidence vote in the parliament but the Georgian Dream coalition could draw support from some 16 independent lawmakers.

-'Democracy in danger'-

Shortly after he was sacked, Foreign Minister Maia Panjikidze said that she and her four deputies were resigning "to show what threats the country is facing."

Alexi Petriashvili, the minister for European and Euro-Atlantic Integration and a close ally of Alasania, also resigned in protest on Tuesday.

"Dictatorship is coming to Georgia, our democracy is in danger," Petriashvili said late on Tuesday.

Georgia's pro-Western President Giorgi Margvelashvili denounced the "political confrontation that endangers the functioning of state institutions and the country's Euro-Atlantic integration."

The US ambassador to Georgia, Richard Norland, said he was concerned that recent legal action against Georgian officials could pursue political ends.

"The number and scope of prosecutions of former and current officials raises legitimate concern that the judicial system is being used in a politicised way, or for political purposes," the diplomat said.

Georgian Dream coalition was assembled by former prime minister and billionaire tycoon Bidzina Ivanishvili, who came to power in 2012, ending a decade-long rule of the pro-Western president Mikheil Saakashvili and his United National Movement (UNM) party.

Scores of former top Saakashvili officials have been arrested and thousands of UNM supporters interrogated over the last two years for alleged wrongdoing, prompting warnings from the West over selective justice and persecution of political opponents.

Ivanishvili stepped down in 2013 and chose his protege Garibashvili to take over as premier, but the tycoon is widely believed to continue to wield power over the tiny Caucasus nation behind the scenes.