Belgian police have killed two men who opened fire on them during one of about a dozen raids against an Islamist group that federal prosecutors said was about to launch “terrorist attacks on a grand scale”.

Coming a week after Islamist gunmen killed 17 people in Paris, the incident heightened fears across Europe of young local Muslims returning radicalised from Syria.

But prosecutor Eric Van Der Sypt said the Belgian probe had been under way before the January 7 attack on French satirical newspaper Charlie Hebdo.

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A third man was detained in the eastern city of Verviers, where police commandos ran into a hail of gunfire after trying to gain entry to an apartment above a town centre bakery.

“The suspects immediately and for several minutes opened fire with military weaponry and handguns on the special units of the federal police before they were neutralised,” Mr Van Der Sypt said.

Public television RTBF showed video of a building at night lit up by flames, with the sound of shots being fired.

Marie Laure from Verviers told RTBF she was in the street with her children when a police commando told them to run for cover.

“When we began running. We heard three or four big explosions and shots,” she said. “It was really startling.”

All three suspects were citizens of Belgium, which has one of the biggest concentrations of European Islamists fighting in Syria.

Other raids on the homes of men returned from the civil war there were conducted across the country, Mr Van Der Sypt said, adding that they were suspected of planning attacks on Belgian police stations.

Security had been tightened at such sites.

“The searches were carried out as part of an investigation into an operational cell, some of whose members had returned from Syria,” he said.

“For the time being, there is no connection with the attacks in Paris.”

Earlier in the day, prosecutors said they had detained a man in southern Belgium whom they suspected of supplying weaponry to Amedy Coulibaly, the killer of four people at a Paris Jewish grocery store after the Charlie Hebdo attack.

After the violence in Verviers, La Meuse newspaper quoted an unidentified police officer saying: “We’ve averted a Belgian Charlie Hebdo.”

Two French brothers, Cherif and Said Kouachi, who like Coulibaly claimed allegiance to Islamist militants in the Middle East, killed 12 people at the offices of Charlie Hebdo.

Overnight, private family funerals were held for five victims of the Charlie Hebdo attack in Paris, including cartoonists Georges Wolinski and Bernard “Tignous” Verlhac.

The latest edition of satirical magazine has sold out in France, sparking fury in some parts of the Muslim world for depicting the Prophet Mohammed.

Per head of population, Belgium is the European country from where the highest number of citizens have taken part in fighting with Syrian rebels in the past four years, data compiled by security researchers have shown.

Belgium has taken a lead in EU efforts to counter the threat perceived from the return of foreign fighters from Syria.

The Belgian government believes about 100 of its nationals have come back from there, while a further 40 may have been killed and about 170 are still in the ranks of fighters in Syria and Iraq.

Belgium is part of the US-led coalition fighting Islamic State and has six F-16 aircraft taking part in bombing raids on Syria and Iraq.

A court in Antwerp is due to deliver its verdict on 46 people accused of recruiting young men to join jihadists or of becoming jihadists in Syria, Belgium’s largest Islamist militant trial to date.

The court was to have given its verdict this week, but it was delayed for a month after the Paris violence.

In Germany, police arrested a suspected supporter of the insurgent group Islamic State who was recently in Syria, federal prosecutors said.