Saif al-Islam Gaddafi, son of former Libyan leader Moamer Gaddafi, was killed Tuesday in an attack at his home in Zintan, according to his political office.

The office said four masked gunmen stormed the residence and carried out what it called a “treacherous and cowardly” assassination.

His lawyer confirmed he was killed at home, while reports said he was shot in the garden of the property.

Speculation has emerged about the possible involvement of militias linked to Libya’s Tripoli-based government, though a militia tied to the defence ministry denied any role, DPA International has reported.

Saif al-Islam had reportedly been preparing a political comeback, and his office is calling for an independent international investigation into his killing.