CAIRO (Reuters) - A prominent Egyptian blogger convicted of insulting Islamist president Mohamed Mursi is facing fresh charges of inciting violence, judicial sources said on Tuesday, in a case that has triggered accusations of a crackdown on dissent.

Ahmed Douma was sentenced to six months in jail on Monday for calling Mursi a criminal and a murderer in media interviews.

He was initially allowed to pay 5,000 Egyptian pounds ($720) bail to leave prison pending an appeal, but the new charge meant he would now stay behind bars, state media reported.

The case has enraged pro-democracy activists who have accused Mursi of using the same restrictive practices as his predecessor Hosni Mubarak, who was ousted in a popular revolt in 2011.

Douma's supporters called for a demonstration on Wednesday in front of the High Court to call for his release.

"It is clear that there is an attack against Ahmed Douma, especially ... They want to send a message to all the youth of the revolution through him," his lawyer Ali Soliman said.

Mursi and his allies in the Muslim Brotherhood movement that propelled him to power have dismissed the accusations and say he believes in free media and speech.

Douma was originally charged with insulting the president in March in the aftermath of deadly clashes in February between locals and police in the Suez Canal city of Port Said.

"Douma will not leave prison before he appears in front of South Cairo's prosecution for questioning on charges of inciting violence in front of the Muslim Brotherhood's office in Muqattam," a judicial source was quoted as saying in al-Ahram state newspaper.

Douma and four other activists are accused of inciting aggression, destruction of property and disturbing civil peace during protests near the Muslim Brotherhood's headquarters in March, when at least 130 people were hospitalized, state media has reported.

(Reporting by Asma Alsharif; Editing by Andrew Heavens)