The United States on Sunday voiced concern over Georgian authorities' decision to call former President Mikheil Saakashvili for questioning in multiple criminal investigations.

"No one is above the law, but launching multiple simultaneous investigations involving a former president raises legitimate concerns about political retribution, particularly when legal and judicial institutions are still fragile," State Department spokeswoman Marie Harf said in a statement.

Prosecutors in Georgia announced on Saturday that they had summoned Saakashvili for questioning on Thursday over a number of criminal cases, including a possible probe into the 2005 death of then Prime Minister Zurab Zhvania.

The country's current Prime Minister Irakli Garibashvili has threatened to put the former president on a wanted list in case of his failure to appear.

Saakashvili, a US ally, is not in Georgia as he left the country soon after his second term ended in November last year. Prosecutors have filed charges against several of his allies.

"As discussed at the highest levels when Prime Minister Garibashvili visited Washington in February, the United States urges Georgia's leaders to focus the nation's energies on the future, a strong economy, continued reform of the justice sector, and rapid progress on Euro-Atlantic integration," Harf said.