TBILISI -- Georgia's opposition parties have warned they will abandon a foreign-brokered deal on election reforms if "political prisoners" are not released.

The ruling and opposition parties on March 8 signed a memorandum of understanding in which they agreed, among other things, that parliament should consist of 120 members elected through a proportional voting system, while 30 members would be elected through a majority system.

The sides have since failed to move forward ahead of parliamentary elections set for October.

In a joint statement on May 13, the opposition parties urged the ruling Georgian Dream party to fulfill the agreement, which they said included the release of "political prisoners."

They also warned that "opposition factions will continue boycotting parliamentary sessions" if their demand is not met.

The opposition claims the release of several jailed politicians who they say have been convicted on politically motivated charges was a condition of the deal.

Georgian Dream representatives have denied that.

Earlier this week, the U.S. and European Union ambassadors called on the ruling and opposition parties to uphold and implement the deal, saying it was intended to "depolarize" Georgia’s political system and "create a better environment" for the upcoming parliamentary elections.

The March 8 deal facilitated by U.S. and the EU officials also says that the party or candidate winning more than 50 percent of the vote in a constituency is awarded the contested parliamentary seat.

Under the accord, the electoral threshold for proportional elections will be set at 1 percent and a capping mechanism will mean that no single party receiving less than 40 percent of the votes cast will be allowed to hold a majority of seats in parliament.

Under the current electoral system, 73 of 150 parliamentary seats are claimed by candidates who finish first in district races. The remaining seats are distributed proportionally to the national share of the vote that a party wins.

This led to Georgian Dream, led by billionaire founder Bidzina Ivanishvili, winning 76 percent of the legislature's seats even though it won just less than half of the popular vote.