Authorities say two policemen were injured and nine people were arrested during a night of clashes between rioting youths and police in central Athens after a demonstration by hundreds of anarchists calling for the closure of a maximum-security prison.

Police said Wednesday the arrests were made on charges including attempted grievous bodily harm, arson and vandalism. A further 21 people were temporarily detained.

Tuesday night's clashes saw dozens of youths throwing petrol bombs and stones at police, who responded with tear gas. At least two cars were burnt.

Anarchists want authorities to close a prison where many convicted militant anarchists are held — and have continued their protests despite pledges to do so from the new radical left-led government elected in January.