CAIRO (Reuters) - Egyptian police arrested seven people on Monday after they were seen raising a rainbow flag at a concert, security sources said, in a rare public show of support for lesbian, gay, bisexual and transgender rights in the conservative Muslim country. Security sources said the seven were arrested for  promoting sexual deviancy,  a euphemism in Egypt for homosexuality, after they were seen on camera raising the rainbow flag at a Mashrou  Leila concert, a popular Lebanese alternative rock band whose lead singer is openly gay. Egyptian Public Prosecutor Nabil Sadek ordered the State Security Prosecution to immediately investigate the incident, state news agency MENA reported. The public prosecutor has not yet announced a decision on whether formal charges will be filed and a case brought to court. Although homosexuality is not specifically outlawed in Egypt, it is a conservative society and discrimination is rife. Gay men are frequently arrested and typically charged with debauchery, immorality or blasphemy. The largest crackdown on homosexuals in Egypt took place in 2001, when police raided a floating disco called the Queen Boat. Fifty-two men were tried in the case, which drew widespread criticism from human rights groups and Western governments. 