Fears that al-Qaeda is planning an attack on the nuclear industry in Europe were renewed yesterday after French secret agents arrested a physicist working at an atomic research centre.

The 32-year-old man, who was detained with his brother, 25, is suspected of providing a list of terrorist targets to North African Islamic radicals. He worked for the European Organisation for Nuclear Research (CERN) in Geneva, Switzerland, according to French police sources.

Agents were said to have intercepted messages in which the physicist, a Frenchman of Algerian origin, had suggested targets in France.

He is believed to have been in contact with members of al-Qaeda in the Islamic Maghreb, an Algerian-based terror organisation that joined Osama bin Laden’s network in 2007.

“He had expressed a wish or a desire to commit terrorist actions but had not materially prepared them,” an intelligence source said.

After he was identified, during an investigation into a French network that had sent Islamic radicals to Afghanistan, the man was put under surveillance for about 18 months. Last month Judge Christophe Teissier, an investigating magistrate specialising in terrorism, opened a formal inquiry into his activities.

The brothers apparently came to the attention of the secret services when agents monitored the internet as part of the inquiry into the recruitment of extremists to fight in Afghanistan. Several exchanges were recorded between the brothers and suspected al-Qaeda contacts.

The pair were arrested by the Central Directorate of Interior Intelligence (DCRI) at their home in Vienne, eastern France. Police seized two computers, three hard discs and two USB keys.

The men were taken for questioning at the directorate’s headquarters in Levallois-Perret, outside Paris. “Perhaps we have avoided the worst possible scenario,” Brice Hortefeux, the French Interior Minister, said. “We are in a situation of permanent vigilance and we follow the declarations of the leaders of certain organisations day by day. Our vigilance is never lowered. The risk is permanent.”

CERN, the leading European laboratory for the study of sub-atomic physics, said that the suspect had never been in contact with any elements that could be used for terrorist purposes.

The man who was arrested worked on analysis concerning the Large Hadron Collider but was not an employee of CERN and “performed his research under a contract with an outside institute”. None of his research had a potential military application, the organisation added.

In its previous incarnation as the Salafist Group for Preaching and Combat, al-Qaeda in the Islamic Maghreb fought the Algerian authorities in an attempt to install an Islamic state at the cost of tens of thousands of lives in the 1990s.

Since joining al-Qaeda it has spread its activities to countries such as Mali, Niger and Mauritania. In June it claimed responsibility for the killing of Christopher Leggett, an American humanitarian worker, in Mauritania.

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