A French official says a suspect has been arrested in connection with four murders outside Paris that authorities fear may be the work of a serial killer.

Prosecutors have said that the same semiautomatic gun was used in all four attacks in the Essonne region and that two victims lived in the same building.

The official, who is close to the investigation, said police were also conducting searches following today's arrest.

France is on alert after a string of shootings last month in the south west that police say was the work of an Islamist militant. That suspect was shot dead in a stand-off with security forces.

In the Essonne killings, authorities have stressed there's no evidence of a link to terrorism.

Later, a judicial official said another person was in custody, without specifying when the suspect was taken in.

In the Essonne killings, the first victim was killed in November; a suspect was detained in that crime but has since retracted his confession. The most recent murder was April 5, after which authorities said they weren't sure if just one person was behind the killings.