An Egyptian man arrested for raising a rainbow flag in support of gay rights at a concert has been ordered to remain in jail for another 15 days, according to reports.

The man, known only as ''Ahmed A", was charged with belonging to an illegal group and spreading ideas that are ''incitement to dissolution and immorality'', news agency Anda said, citing local reports. The decision was taken by the prosecutor's office for State Security.

Ahmed A is among dozens of people arrested after they raised rainbow flags – a symbol that represents the LGBT community – at a concert by rock band Mashrou' Leila in Cairo on 22 September.

The incident sparked a crackdown on people believed to be gay or supportive of gay rights.

Although homosexuality is not illegal in Egypt, the country's laws only recognise unions between a man and a woman as legal. Members of the LGBT community face discrimination, violence and arrests in the nation.

Rights groups have called on the Egyptian government to halt the persecution of gay activists.

The Egyptian Initiative for Personal Rights (EIPR) said police have arrested at least 57 people so far, sometimes after luring them to hotel rooms with dating app Grindr.

Rights groups claimed some of those arrested were subjected to anal examinations to determine whether they had engaged in same-sex intercourse.

Human Rights Watch (HRW) and Amnesty International called on the government to halt the "abhorrent" procedure, which they said amounts to torture.

Government officials rejected the claims.

"Allegations of torturing or insulting those medically examined are lies not worth responding to. The examinations are carried out by a forensic doctor who swore to respect his profession and its ethics," one judicial source was quoted by Reuters as saying.

Following the incident at the concert, local media reported that the government was in talks to discuss the option to criminalise homosexuality.

A draft law received approval from a number of the parliament's members, the Egypt Independent reported earlier in October.