Belgian police inspect the entrance of an apartment in central Verviers, a town between Liege and the German border, in the east of Belgium January 15, 2015. At least two people were killed when Belgian counter-terrorist police raided an apartment used by suspected Islamist radicals on Thursday, local media said, describing a coordinated, national operation related to last week's attacks in Paris. Judiciary officials confirmed only that a counter-terrorism operation took place in Verviers. [Photo/Agencies]

ISLAMIST STRENGTH

Belgian Prime Minister Charles Michel raised the national alert level to three from two on a four-point scale. "We are not aware of any specific or concrete threats, however, in the situation we can consider it is useful to raise the level of prudence and vigilance," he told Reuters.

With half a million Muslims, mostly of French-speaking North African descent, among its 11 million people, Belgium has seen similar discontent to that in France among young, unemployed children of immigrants in blighted, post-industrial towns like Verviers, once a major centre for wool and other textile mills.

A young Frenchman of Algerian origin is facing trial in Belgium, accused of shooting dead four people at the Jewish Museum in the capital Brussels last May.

Per head of population, more Belgians have taken part in the fighting in Syria than any other European state. The Belgian government believes about 100 of its nationals have come back with combat experience. A further 40 may have been killed and about 170 are still in the ranks of fighters in Syria and Iraq.

Public television RTBF showed video from Verviers of a building at night lit up by flames, with the sound of shots being fired. Late into the evening, police commandos were controlling some streets and checking other sites. Crime scene investigators were at work.

Emrick Bertholet was outside a pharmacy shortly before 6 p.m. (1700 GMT) when police vehicles roared up and armed commandos leapt out: "They shouted 'Let's go', they ran off and everything happened really quickly," he told Reuters.

"I heard the sound of grenades, bursts of gunfire ... I'm a bit shocked, a bit afraid, surprised it could happen here."

Belgium has taken a lead in EU efforts to counter the threat perceived from the return of "foreign fighters" from Syria. It is also part of the U.S.-led coalition fighting Islamic State. Six Belgian F-16s have taken part in bombing 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.

German police said on Friday they had arrested two people following a raid on 12 homes and a mosque group linked to radical Islamic Salafists. The arrests followed months of investigation into five Turks suspected of "preparing a serious act of violence against the state in Syria".

A police spokesman said the suspects were probably part of an extremist cell that had recruited fighters for Syria.

French police arrested a dozen people suspected of helping the Islamist militant gunmen in last week's Paris killings.