Egypt extended Thursday by 15 days the detention of three journalists working for Al-Jazeera television network who the authorities accuse of threatening public order, one of their lawyers said. Australian Peter Greste, the Canadian-Egyptian bureau chief for Jazeera English in Cairo Mohammed Fahmy and producer Baher Mohamed, were arrested on December 29 in a Cairo hotel. Ragia Omran, a lawyer representing Greste, told AFP that their detention has been extended by "15 days pending investigation". The prosecution has accused them of "filming security installations, threatening public order and peace, and working without a permit" in Egypt. It also accused Fahmy of belonging to a "terrorist" group, saying he was a member of the Islamist Muslim Brotherhood, which has beendesignated as a terrorist organisation by the authorities. Fahmy, a well-known journalist in Cairo who previously worked with CNN, has no known ties with the Brotherhood. Greste formerly worked with the BBC and won the prestigious Peabody Award in 2011 for a documentary on Somalia. The prosecution has also accused the three of "supporting (the Brotherhood) with equipment, information and recordings that promoted its interest". The Qatar-based Al-Jazeera issued a statement on Thursday calling on Egypt "to release immediately and with no conditions" its journalists. Al-Jazeera spokesman Ghassan Abu Hussein said their detention was an attempt to "gag and obstruct" the network's media activities. Two other Al-Jazeera reporters remain in detention, including Abdullah Elshamy of the Arabic language station arrested on August 14 when police dispersed an Islamist protest camp in Cairo, killing hundreds in clashes. Egyptian authorities have been incensed with Al-Jazeera's coverage of a police crackdown on the Muslim Brotherhood of ousted presidentMohamed Morsi who was overthrown by the army in July. The government declared the Brotherhood a "terrorist organisation" in December, after accusing it of a suicide car bombing at a police headquarters north of Cairo that killed 15 people. The blacklisting also means that promoting the Brotherhood verbally or in writing is illegal and can lead to harsh and lengthy prison sentences.