Shiite Muslims flagellate themselves with knives on chains during an annual prayer ritual at Athens' main port of Piraeus on Monday March 1, 2004. (AP)

[1] ATHENS, Greece - Greek police have increased scrutiny of Muslim immigrant groups and makeshift mosques in Athens — a city with no official place of worship for Muslims — ahead of the Olympics.

The surveillance, confirmed to The Associated Press by police sources, was intensified following the deadly train bombings in Madrid on March 11 and seeks to gain insights into Greece's small and often insular communities of nonnative Muslims.