CAIRO - Egypt's Muslims have formed human shields near Orthodox churches as Copts celebrate their Christmas. Egypt's authorities had to tighten security after a New Year's Day bombing had killed 21. On Christmas Eve drivers were banned from parking in front of churches. Blocks near temples were being monitored by explosives detection teams and policemen. Copts use Julian calendar according to which Christmas Day falls on January 7. At least 70,000 officers and conscripts had been deployed across the country to secure worshippers as they attended Christmas Eve mass. According to police, a primitive explosive device was found in a church in the southern city of Minya but it turned out to be detonator free.