French police have detained three people in an investigation into an alleged plot to attack a church near Paris, authorities said Sunday.

The three are suspected of possible links to Sid Ahmed Ghlam, the chief suspect in the thwarted attack. The investigation has revived security concerns in France, tense after deadly attacks on a kosher market and newspaper offices in January.

Authorities say Ghlam, an Algerian computer science student, planned an attack on a church in Villejuif, south of Paris, and is suspected in the killing of a woman nearby. He was arrested last week after apparently shooting himself by accident.

He was handed preliminary charges, including one for killing in relation to a terrorist enterprise -- which means investigators believe he had accomplices.

As of Sunday evening, a French security official said three other suspects are in custody in the case: One man, whose DNA was found in Ghlam's bedroom, one whose DNA was found on a hairbrush in Ghlam's house, and another who may have provided logistical support for the alleged plot. The official wasn't authorized to be publicly named.

The Paris prosecutor's office confirmed that suspects are in custody but wouldn't provide further details. It is unclear at this stage whether the three suspects were involved in the purported plot.

A search of Ghlam's home turned up three Kalashnikov assault rifles as well as phones and computers that indicate he had been in contact with someone possibly located in Syria, who urged the suspect to target a church, according to the prosecutor. Police also found Arabic-language material that mentioned Al Qaeda and the Islamic State group, but so far there is no evidence he had direct ties to any organized groups.