Tension was reported on Tuesday morning in an inner city neighbourhood of Athens after local residents attempted to block the holding of a mass outdoor prayer by Muslims, mostly migrants from the Middle East and South Asia, in the district's main square.

Riot police arrived on the scene at daybreak, while the outdoor prayer was later interrupted and cancelled. Residents were seen waving Greek flags on balconies, while some people even threw eggs.

The square, across from the Attiki electric rail station, is close to the congested inner city neighbourhood of Aghios Panteleimonas, where local residents have angrily railed against the presence of large numbers of illegal immigrants in their area, charging a significant increase in crime and a downgrading of the precinct.

Repeated incidents have also attracted increased local media attention, especially following the presence of ultra-nationalist and neo-fascist elements in the district. The latter development has increased worries that extremist political elements are exploiting local residents' anger over conditions in the district.

A handful of outdoor prayers were reported in other parts of the Greek capital, including in front of the Athens University's 19th century neo-classical administrative building, where the status of "university asylum" exists.

Similar tensions have been recorded over the recent period in several parts of downtown Athens, as the predominately eastern Orthodox Christian country of 11 million on SE Europe's periphery struggles to deal with an increasing flow of illegal migrants -- now mostly hailing from Third World countries in the Mideast, South Asia and even Africa -- attempting to sneak into Greece from neighbouring EU hopeful Turkey.

The only native-born Muslims in Greece are mostly centred in the extreme northeast province of Thrace, Greece's only land border with Turkey.

Police estimated the number of people gathered in 12 different locations of greater Athens at 13,000, with some 600 Muslims reported in the Attiki square site.

Tuesday marked the Eid al-Adha commemoration in the Muslim world.