TBILISI, Georgia — Concerned that Georgia’s bitter political transition could turn into a wave of political reprisals, American officials have urged the new prime minister to stop the arrests of officials who served under President Mikheil Saakashvili, warning that politically motivated prosecutions could jeopardize Georgia’s chances of joining NATO.

But a court in Tbilisi decided over the weekend to leave 12 Interior Ministry officials in detention pending their trial. The officials are accused of using illegal surveillance to record conversations discrediting Bidzina Ivanishvili, whose party defeated Mr. Saakashvili’s in parliamentary elections last month.

Lawmakers from the rival parties must now share power in Parliament, but Mr. Ivanishvili, the new prime minister, said he would make it a priority to investigate officials leaving the government of Mr. Saakashvili, whose term ends next year.

Philip H. Gordon, the assistant secretary of state for European and Eurasian affairs, met with Mr. Ivanishvili on Friday and said that Georgia’s transfer of power was seen as “in some ways a model for the region.” But Mr. Gordon warned that prosecutions of officials who served under Mr. Saakashvili could be viewed as political payback.