Counterterrorism police in France have opened an investigation into a knife attack which saw at least two people wounded near the former offices of satirical newspaper Charlie Hebdo on Friday.

The investigation was opened into “attempted murder in relation with a terrorist enterprise,” according to an official at the prosecutor’s office.

One suspect has been arrested.

A police official said that while authorities initially thought two attackers were involved, they now believe it was only one person, who was detained near the Bastille plaza in eastern Paris.

A blade was found at the scene, two police sources told Reuters. One described it as a machete, the other called it a meat cleaver.

It is unclear what motivated the attack Friday or whether it had any link to Charlie Hebdo, which moved offices after they were attacked by Islamic extremists in 2015.

Police did not release the identities of the attacker or the wounded, who are in “absolutely urgent” condition, the official said. 

Prime Minister Jean Castex cut short a visit to a suburb north of Paris to head to the Interior Ministry to follow developments.

The trial in the Charlie Hebdo attacks is currently underway in the same city. Murmurs broke at the terrorism trial of 14 people, including three fugitives, accused of helping the attackers in the January 2015 killings, as the news filtered through. The widows of the Charlie Hebdo attackers are scheduled to testify Friday afternoon.