Belgian police arrested two men suspected of plotting a terror attack in Belgium as Europe remained on edge Saturday following a rising wave of militant bloodshed on the continent.

Police arrested two men, identified as Noureddine H. and his brother Hamza H., after house searches late Friday in Belgium's French-speaking areas of Mons and Liege, federal prosecutors said.

"Both are suspected of planning a terrorist attack somewhere in Belgium," a spokesman said in an English version of the statement. The French version referred to "planning attacks" in the plural.

The prosecutor's office said there was for now no connection with the bombings on March 22 at Brussels airport and a metro station near the European Union headquarters that left 32 people dead.

Those attacks were claimed by the Daish militant group which is waging war in Syria and Iraq.

No weapons or explosives were found in Friday's raids ordered by a judge specialising in counter-terror cases, it said.

A judge will review the arrests of the brothers later Saturday and decide whether to keep them in custody.

Several of those involved in the Brussels bloodshed were directly linked to the November 13 bombing and gun attacks in Paris which left 130 dead and were also claimed by the Islamic State.

Belgian authorities last month charged two men with terrorist offences amid reports of a planned attack on a Euro 2016 fanzone in central Brussels.

Belgium then beefed up security for its July 21 national day celebrations after the truck attack that killed 84 people in the French city of Nice on Bastille Day, July 14.

The authorities in Belgium, which hosts the headquarters of the 28-nation EU and the North Atlantic Treaty Organisation, had previously anticipated a possible truck-style attack before the Nice carnage.

Tensions have risen further after a week of attacks in Germany, some claimed by Daish, that left 13 people dead, including three assailants, and dozens wounded.

Belgium is the main source per head of population of jihadist recruits going from the European Union to fight with Daish in Syria, causing deep concern that they will return home battle-hardened and even more radicalised.

The interior ministry said 457 Belgian men and women have gone or tried to join militants in the Middle East, including 90 who are missing or dead.

- False alerts -

Belgium's massive security deployment that includes armed soldiers on its streets has also responded to two alerts in the last few weeks in central Brussels that turned out to be false.

One involved an Iranian student studying radiation and another a man with psychiatric problems who was carrying a fake suicide belt full of salt and biscuits.

In less than two weeks in July, Daish jihadists claimed four bloody assaults in France and Germany.

Experts say each attack can inspire another, with militants egged on further by the media spotlight the atrocities attract.

The attacks come as Europe grapples with long-term economic problems, the Greek debt standoff, the migrant crisis that saw more than a million people stream into Europe in 2015, and Britain's shock vote to quit the European Union.