The European Commission headquarters in Brussels was going to be the target of an alleged terrorist plot, according to media reports.

Flemish newspaper Het Laatste Nieuws on Monday (22 September) say police found a cache of weapons and explosives in an apartment in Brussels.

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One of the two suspects, both Dutch nationals of Turkish origin, is said to have links to Shariah4Belgium, a Belgian radical Salafist organisation.

The couple, said to be residents in The Hague, were detained early August at the Brussels airport after returning from Syria via Turkey.

A European Commission spokesperson said they are aware of the plot but had received no warnings or threats, reports the Guardian.

Authorities, for their part, are increasingly stepping up efforts to contain possible threats from returning nationals who have fought alongside Islamist militia groups in Syria and Iraq.

Governments are concerned some of the more radical may be seeking to stage attacks on their home turf.

In Belgium, around a quarter of the 400 nationals who have left to fight have since returned. Most are entering the warzone in Syria through by crossing over the Turkish border.

Belgian paper L’Echo says police are actively tracking around 90 of the returned fighters.

"Our starting point is that among them, one out of nine aim to carry out an attack,” an unnamed source told the paper.

“That is a conservative estimate, if you also take into account the people who help them,” added the source.

Some are said to have joined the Islamic State (Isis), the extremist group behind recent beheadings of reporters and aid workers.

The revelations about the commission come on the heels of an earlier terror attack in the Belgian capital over the summer where a gunman killed four people at the Jewish Museum.

French national Mehdi Nemmouche is suspected to behind the gun killings and is now awaiting trial on "terrorist murder" charges.

The 29-year old was arrested in late May in Marseilles and is said to have links with radical militia groups after having spent a year in Syria.