Belgian police are holding 20 youths of North African descent after two nights of rioting in the country's second city, Antwerp.

The violence began after a man of Moroccan origin, 27-year-old schoolteacher Mohammed Achrak, was shot dead by his neighbour on Tuesday.

Police arrested more than 100 youths but later released most of them, warning that they would be maintaining a zero tolerance policy in the Borgerhout district.

More than 100 people were arrested over the disturbance

The authorities have said there were no indications the killing was a racist act, but the protesters dispute this.

A neighbour told the BBC he believed the alleged killer was a racist.

"He intimidated me four or five months ago. He did not want any Moroccans living in his building. He said: 'I'll shoot the first person I see.' I didn't take him seriously, I thought 'he can't be serious'. He's a racist, he hates Arabs."

A 66-year-old pensioner has been charged with the murder.

Prosecutors say he appears mentally unstable.

Far-right stronghold

Police say more than 100 young men - mainly of Arab origin - took to the streets on Tuesday night and again Wednesday, smashing windows and throwing stones at officers.

"Most of the arrests were for throwing stones, attacking the police and buses and trams," a police spokeswoman said.

Elders of the Muslim community tried to calm the crowd.

Officials said members of the European Arab League - a group that last week set up patrols in the streets of Antwerp to ensure police officers did not discriminate against residents of Arab origin - did little to discourage the riot.

About 30,000 residents of Arab origin live in Antwerp, where the Belgian far-right opposition Vlaams Blok party won 33% of the vote in the last municipal elections.