By Margarita Antidze

TBILISI (Reuters) - The Georgian government detained the armed forces' chief of staff on Wednesday on suspicion of abuse of power, stepping up what the opposition says is political persecution of President Mikheil Saakashvili's allies.

New Prime Minister Bidzina Ivanishvili's coalition said after ousting Saakashvili's party in an election last month that former officials suspected of crimes would be prosecuted.

It began acting on its promise on Tuesday by detaining Bacho Akhalaia, a former interior and defense minister. General Georgy Kalandadze, the military chief of staff, and another army commander were brought in for questioning early on Wednesday.

The opposition fears a witch hunt now that Saakashvili's nine-year dominance has ended in the former Soviet republic, a focus of tensions between Russia and the West and a transit country for Caspian Sea oil and gas exports to Europe.

Akhalaia, who quit as interior minister over a prison abuse scandal shortly before the election, remained in detention at the prosecutor general's office after being questioned for three hours, his lawyer said.

"The reason for his detention was that during his work as a defense minister he allegedly insulted several officers in the presence of others," attorney David Dekanoidze told reporters.

"I've never ever heard such an absurd reason for detention," Dekanoidze said.

Chief prosecutor Archil Kbilashvili said Kalandadze and Zurab Shamatava, commander of the army's Fourth Brigade, faced similar accusations. He said state investigators had evidence that Akhalaia, Kalandadze and Shamatava had insulted six servicemen in October 2011.

None of the detainees has been charged but could face up to eight years in jail if found guilty of abuse of power.

"THE ACTION OF COWARDS"

Akhalaia left Georgia after the election but returned this week, saying he was ready to answer any questions from law-enforcement agencies.

"Akhalaia's detention is the action of cowards. They got very scared when Bacho Akhalaia, an honest man, returned to Georgia," said Akaky Minashvili, a member of parliament from Saakashvili's United National Movement (UNM).

The opposition fears retribution after the closely fought election and says Ivanishvili hopes to put pressure on his rival Saakashvili. In one such move, Ivanishvili said last week the government was considering cutting funding for the presidential administration next year.

"It's nothing but political persecution," Nugzar Tsiklauri, a member of parliament from the UNM, said of the detentions.

Saakashvili, the hero of the 2003 Rose Revolution that swept out Georgia's post-Soviet old guard, must step down next year and reforms due to take effect after a presidential vote in 2013 will weaken the president and strengthen parliament and the prime minister.

Akhalaia, 32, was appointed as Georgia's defense minister in 2009, one year after a five-day war with Russia, and served in that post for three years.

Before that he served as the head of Georgia's penitentiary department, where he led a struggle against the established system of "thieves in law" which ruled prisons in the former Soviet republic.

Human rights groups have accused Akhalaia of a carrying out a heavy-handed crackdown on Georgia's largest prison riot in 2006, in which seven inmates were killed, and blamed him for the ill treatment of prisoners and military servicemen.

The reports of prisoner abuse led to protests in the country of 4.5 million just before the election. Akhalaia was one of several former high-ranking officials, including the defense and justice ministers, who left the country after the election.

(Editing by Timothy Heritage and Angus MacSwan)