( BRUSSELS ) - Hundreds of Iranian opposition supporters rallied in the European quarter of Brussels Saturday calling for a re-run of the contested presidential election and the release of political prisoners.

At least 500 people -- 1,000 according to organisers -- gathered near the main EU buildings in the Belgian capital, many carrying placards or photographs showing suspected election-related unrest.

Some were draped in Iranian flags, while others wore T-shirts marked "Where Is My Vote?". Banners were marked "Stop Death and Terror in Iran" or "Revolution is the Only Solution".

The crowd, from Belgium and neighbouring countries like Germany and the Netherlands, was drawn together by rights and student groups and chanted "Freedom, freedom in Iran", and "Down with the dictators".

A handful of police officers watched from inside a van around 100 metres (yards) away, as a concert of Iranian musicians got underway.

The rally came amid the biggest unrest in the Islamic republic since the revolution in 1979, sparked by a June 12 election that returned President Mahmoud Ahmadinejad to power and which the opposition claims was rigged.

On Friday, European Union governments called in Iranian envoys across the 27-nation bloc in protest at the detention of British embassy staff accused by the authorities there of stoking the unrest.