Two Italian hostages were freed in Libya and flown back to Italy on Sunday, after two of their fellow captives were reportedly killed by ISIS militants, officials said.

The four captives were employees of an Italian construction company Bonatti and were detained last July near the western Libyan city of Sabratha, near a compound owned by the energy group Eni. Gino Pollicardo and Filippo Calcagno were transferred by helicopter to Tripoli from Sabratha at night and later boarded an Italian plane, Libyan officials said.

They arrived at Rome’s military airport of Ciampino and were due to be interrogated by judicial officers, Italian media declared.

According to a spokesman for Libyan security forces in Sabratha, fellow captives Salvatore Failla and Fausto Piano were shot dead by ISIS militants shortly before Libyan forces attacked them on Wednesday.

The spokesman, Sabri Kshada, has said Pollicardo and Calcagno were released during a raid early on Friday.However the exact settings of both the killings and the release remain uncertain. The two freed hostages have made no comment.

Sabratha is one of several Libyan cities in which militants loyal to ISIS have established a presence, taking advantage of the chaos that has plagued Libya since Muammar Gaddafi was toppled in an uprising five years ago.

Pollicardo and Calcagno were questioned by Libyan forces at Tripoli’s Mitiga airport for about 45 minutes before departing for Italy and briefly appeared beside Ali Abu Zakouk, the foreign minister of Tripoli’s self-declared government.

“We need support and cooperation from the Italians to tackle the criminal organization of ISIS in Libya,” Zakouk said, without giving details on how the hostages were released.