PARIS — The French counterterrorism prosecutor’s office said Wednesday four individuals are suspected of “terrorist criminal conspiracy” after police thwarted a bomb attack outside a Bank of America building in Paris in a case believed to have links to Iran.

Police arrested one of the suspects outside the bank in the early hours of Saturday morning in front of the building where they found a homemade bomb made up of a gasoline-filled container taped to a powerful firework. Forensic experts said the device contained 650 grams (about 23 ounces) of explosives, an unusually large quantity not previously encountered in France. They said it could have produced a large fireball and ignited a significant blaze.

Prosecutors requested the four suspects, including three minors, to be placed in detention pending trial as it formally opened a judicial investigation into the incident, which follows similar actions across Europe.

A propaganda video that circulated on social media on March 23, just before the planned attack, specifically mentioned the U.S. bank’s offices in Paris as a potential target. It was attributed to a pro-Iran group known as Harakat Ashab al-Yamin al-Islamia, which translates as the Islamic Movement of the Companions of the Right.

The planned attack was uncovered early on Saturday morning, when police officers conducting surveillance outside the bank spotted two individuals near the entrance. Officers arrested a 17-year-old suspect at the scene.

They later arrested two other 16-year old suspects and one adult previously convicted of drug trafficking. A fifth person was released without charge.

The three minors, who have no prior criminal records, have denied any terror-related intent, the prosecutor’s office said.

The judicial investigation was opened on preliminary charges of terrorist criminal conspiracy, building, possessing and transporting an explosive device and attempted destruction as part of an organized group and in connection with a terrorist enterprise.

Prosecutors said analysis of CCTV footage, the suspects’ digital media and mobile phone data, as well as their statements to the police showed the three minors were recruited by the adult last week to place and ignite the device at the specified address and film the scene in exchange for 500 to 1,000 euros (about $530 to $1,160).

The Harakat Ashab al-Yamin al-Islamia group claimed responsibility for other actions across Europe including in Belgium and the Netherlands and for an attack last week in London, where four ambulances belonging to a Jewish charity were set on fire.

Counterterrorism police in London announced three additional arrests Wednesday over the ambulance attack. Two men were previously bailed after being detained in the probe.

The prosecutor’s office said the foiled attack in Paris therefore appears “likely linked” to the group “although this has not yet been formally established at this stage of the proceedings.”

Interior Minister Laurent Nuñez said this week Iran’s intelligence services habitually use “proxies,” that is a series of subcontractors, to carry out actions abroad targeting U.S interests, Jewish community and Iranian opposition figures.

French authorities have stepped up security around key personalities and sites since the U.S. and Israel launched their war against Iran on Feb. 28, including personal protection for some people from the Iranian opposition.