PARIS >> A peroxide-based explosive that has been employed by Islamic extremists was found today in an apartment outside Paris that authorities suspect might have been in use as a lab for possible attacks, two French officials said.

A police official told The Associated Press that some 100 grams of usable triacetone triperoxide, better known as TATP, were found in the Villejuif apartment where a police operation was carried out earlier in the day, leading to the detention of two suspects.

A judicial official confirmed that TATP, an explosive used by Islamic State group militants in the past, was found in the unit, but didn’t specify in what quantity.

The two officials with knowledge of the probe spoke on condition of anonymity because of the ongoing investigation.

A tip from a repairman led police to the apartment this morning, Interior Minister Gerard Collomb said in a statement. He was doing a job in the Villejuif building and informed authorities after noticing suspicious products in an apartment.

Police found substances that “may be used to make explosives” in the unit, Collomb said, praising the “civic reflex” of the worker.

The Paris prosecutor’s office said its counter-terrorism section has opened an investigation under potential charges of “criminal terrorist association” and “possession, transportation and production of explosive substances in relation with a terrorist action by an organized gang.”

A bomb-disposal operation was carried out in the apartment, three police officials said. They spoke on condition of anonymity because of the ongoing investigation.

Associated Press reporters in Villejuif saw forensic officers moving around in white uniforms and police vans blocking a large street in the city, which is located just 3 kilometers (less than two miles) south of Paris.