A French judge has arrived in Lithuania to investigate the death of actress Marie Trintignant.
Cantat's custody has been extended to October
Nathalie Turquey is expected to place rock singer Bertrand Cantat, Ms Trintignant's boyfriend who is suspected of causing her death, under investigation for manslaughter.
The measure is a step short of pressing charges against Mr Cantat, who has been held by Lithuanian police since 27 July.
Correspondents say Ms Turquey's visit could be an indication that Lithuania is prepared to extradite Mr Cantat - there is currently no extradition agreement between the two countries.
Sources at the Paris prosecutor's office told Le Monde newspaper that there were no disagreements with Vilnius over the case.
Manslaughter charges carry maximum sentences of 15 years in both countries.
Ms Trintignant was admitted to hospital in a coma suffering head injuries on 27 July.
She was pronounced dead five days later, and a post-mortem examination showed death was caused by severe blows to the head.
Trintignant died after five days in a coma
Mr Cantat says that Ms Trintignant's death was an accident, and that he merely slapped her, causing her to fall over.
The Lithuanian authorities have extended his custody to mid-October pending an investigation.
The 41-year-old lead singer with the band Noir Desir was moved on Thursday to an ordinary jail from prison hospital, where had spent two weeks because of his fragile psychological state.
Ms Trintignant had been in Lithuania making a television film with her director mother Nadine Trintignant when the incident happened.
She had been staying a hotel with Mr Cantat and her 17-year-old son Roman.
She was admitted to hospital where she remained for several days before being flown back to France, where she was kept alive on a life-support machine.
Doctors performed two operations on her brain but were never hopeful of her chances of survival.