Georgia sentenced five senior military officials to seven years in jail on Monday, in a controversial embezzlement case that has heightened political tensions in the Caucasus country ahead of autumn's parliamentary polls.

A court found four serving defence officials and one former official guilty of misspending state funds on a 2013 contract to lay fibre optic cables. They denied any wrongdoing, claiming that the case against them was fabricated.

Opposition parties have claimed the prosecutions were politically motivated and intended to smear former defence minister Irakli Alasania, who is now a popular opposition politician.

"We knew that the government is in control of the courts and the prosecutor's office, but still we didn't expect such an illegal verdict," said Alasania, leader of the Free Democrats party.

Alasania has claimed the case was fabricated to discredit him at the request of former prime minister Bidzina Ivanishvili who has retained significant influence since leaving office.

Alasania was sacked as defence minister and joined the opposition after corruption charges were brought against officials in his department in October 2014.

The ex-minister said that the latest verdict would "put an end to (Ivanishvili's) rule".

Ivanishvili stepped down as prime minister in 2013 but is still widely believed to wield power in the strategic Black Sea nation.

Georgia's main opposition party, the United National Movement (ENM) of ex-president Mikheil Saakashvili, also criticised the verdict.

"(It) shows that the entire judiciary system is subordinated to Ivanishvili," Sergo Ratiani, an ENM party leader, told journalists.

The conflict between billionaire tycoon Ivanishvili and Alasania has been described by observers as an increasingly bitter power struggle.

In March, Alasania accused Ivanishvili of "attacks on politicians" after a covertly filmed sex tape of a Free Democrats politician was posted online.

Georgia's pro-Western President Giorgi Margvelashvili has described the political turmoil as a "threat" to the country.

The United States has expressed concern that such legal action against Georgian officials may be politicised.

Ivanishvili's Georgian Dream party, Saakashvili's United National Movement, and Alasania's Free Democrats will be the main contenders in October's parliamentary polls.