By Margarita Antidze

TBILISI (Reuters) - The United States urged political rivals in Georgia on Friday to work together and avoid selective justice in the prosecution of figures from the ousted government of President Mikheil Saakashvili.

Detentions of former officials since billionaire Bidzina Ivanishvili led an opposition coalition to election victory over Saakashvili's long-ruling party has raised fears of a witch-hunt in the ex-Soviet state.

Washington is eager for stability in Georgia, a route for Caspian Sea oil and gas exports to Europe and a focus of geopolitical rivalry between the West and Russia, which routed Georgian forces in a five-day war in August 2008.

U.S. Assistant Secretary of State Philip Gordon, the highest American official to visit since the October 1 vote, mixed expressions of support for the nation that steered a strongly pro-Western course under Saakashvili with words of caution.

He pointed to potential pitfalls during a period of cohabitation between Ivanishvili and Saakashvili, who swept to power in the peaceful 2003 Rose Revolution and is due to remain in the presidency until an election next year.

"I stressed how important it is and will continue to be for the two sides to work together... We are just stressing to both sides how important it is not to let those tensions stand in the way of the rule of law," Gordon said after meeting Ivanishvili.

Russia increased its military presence in two Moscow-backed breakaway regions of Georgia and recognized them as independent nations after the war, which followed increasing tension over Saakashvili's drive to bring his country into NATO.

Gordon said he told Ivanishvili "how committed the United States is and will remain in terms of our support for Georgia, for its sovereignty and territorial integrity, for its economic development and for the democratic transition that is ongoing."

Ivanishvili told Reuters on Thursday that "from today" he will work closely with his bitter political rival Saakashvili, rejecting suggestions that he has used the courts to settle scores since the election.

PEACEFUL TRANSITION

Ivanishvili, who battled accusations from Saakashvili during the campaign that he is a Russian stooge, has said relations with the United States and Europe are the main priority but that he wants to improve badly strained ties with Russia.

Western nations were relieved at the peaceful transition of power from Saakashvili's party to Ivanishvili's coalition, but a wave of arrests began with the detention last week of Bacho Akhalaia, a former interior and defence minister.

More than ten former senior officials, including the army's acting chief-of-staff and former deputy interior minister, have been arrested and charged with abuse of power, illegal confinement and the illegal obtaining of personal information.

Gordon said investigations and prosecution should be free from any signs of political persecution and "selective justice."

"Nobody wants to see an absence of rule of law and if people are guilty of crimes, those crimes should be investigated and people should be held accountable," said Gordon.

But if the process "looks like or it is designed to go after political adversaries, or it's not done in a transparent way, then the whole country will pay a price," he said.

The head of NATO has expressed concern about the arrests and European officials who Ivanishvili met this week in Brussels criticized cases opened against his political opponents.

Ivanishvili promised to abide by the rule of law.

"We are giving and will be giving clarifications in regard to arrests in order for them not to be perceived as political persecution or selective justice," Ivanishvili said after the meeting with Gordon.

(Reporting by Margarita Antidze; Editing by Steve Gutterman and Tom Pfeiffer)