U.N. judges have ordered a retrial for two former allies of the late Serbian President Slobodan Milosevic who were acquitted in 2013 of setting up and arming notorious Serb paramilitary gangs that committed atrocities in Bosnia and Croatia during the 1990s Balkan wars.

Presiding Judge Fausto Pocar on Tuesday overturned the acquittals of Jovica Stanisic and Franko Simatovic and ordered both men detained pending their new trial.

Stanisic was head of Serbia's state security service until Milosevic fired him in 1998 and Simatovic was his former deputy. Prosecutors said they took part in a criminal plan to drive non-Serbs out of parts of Bosnia and Croatia.

Neither man showed any emotion as Pocar ordered the new trial.