A Lebanese military judge has ordered a re-trial of Lebanese American Amer Fakhoury, who was acquitted on Monday.
Judge Ghassan Khoury asked the Military Court of Appeals to reverse the acquittal and issue an arrest warrant for Fakhoury.
The Lebanese-US citizen was allegedly involved in the torture and murder of several inmates while serving as a prison guard in Khiam prison in southern Lebanon, in the 1980s and 1990s.
Human Rights groups have called the prison a centre for torture, with at least ten people thought to have died during Fakhoury's tenure.
A member of the South Lebanon Army (SLA), an Israeli-backed militia which was disbanded in 2000, Fakhoury is thought to have been nicknamed the "Butcher of Khiam".
The charges against Fakhoury were dropped because the statute of limitations had expired as the alleged offences took place more than a decade ago, state-run National News Agency (NNA) reported on Monday.
However, Khoury has asked for Fakhoury to be re-tried on charges of kidnapping, torturing and detaining Lebanese citizens as well as "killing and attempting to kill others", according to NNA.
One former detainee told L'Orient Le Jour newspaper last year that "[the jailers] used to whip our bodies with electrical cables until our skin got lacerated. Amer Fakhoury was the one who orchestrated the torture sessions".
A travel ban has been issued, forbidding Fakhoury from leaving Lebanon for the next two months. Local media, however, reported that Fakhoury was released and had attempted to leave the country.
The appeal comes after a popular outcry in Lebanon over Fakhoury's acquittal, which sparked prison riots, and protests.
In a statement, Hezbollah said "this is a sad day for Lebanon and justice".
Fakhoury's family and lawyers, however, said that "his position in the Khiam prison was strictly logistical", and that "he had no contact with prisoners".
The Lebanese-American's family have called for Fakhoury's release citing newly diagnosed stage 4 cancer, which has prevented him from attending recent questioning sessions.
The US has pressured Lebanon to release Fakhoury by threatening renewed sanctions against Hezbollah, while Senators Shaheen and Cruz introduced legislation in February which would impose sanctions on Lebanese officials deemed to be involved in the unlawful detention, arrest or abuse of a US citizen.
Fakhoury has been in custody since 12 September, when he returned to Lebanon after more than two decades to visit family.