Some 500 supporters of prominent Salafist preacher and former presidential candidate Hazem Abu-Ismail attacked the headquarters of the opposition Wafd Party on Saturday night, according to Mohamed Tharwat, managing editor of Al-Wafd news website.
Tharwat told the Hayat television channel that attackers surrounded the building, located in Cairo's middle-class Dokki district and sprayed it with fireworks then destroyed cars parked outside the headquarters.
"They destroyed the windows at the building entrance, but didn't enter the building," he said. "Abu Ismail's supporters later clashed with Central Security Forces [CSF], who evacuated the area."
He added: "I hold President Mohamed Mori responsible for what the [Wafd] party has suffered."
Eyewitness Omar Said, an Egyptian reporter for Lebanon's Al-Safir newspaper, said that attackers broke into the building and beat up journalists and Wafd Party members.
As of 10pm local time, Said also said the assailants were still locking horns with the CSF in adjacent streets. "All the attackers are bearded," he told Ahram Online.
Abu-Ismail supporters, known as 'Hazemoun,' have been holding a sit-in at Egypt's Media Production City in Cairo's 6 October City district to protest alleged media bias against Islamist figures and groups in the run-up to Egypt's contentious constitutional referendum.
On several occasions, protesters have threatened to storm the premises of Media Production City if protesters opposed to President Mohamed Morsi's did the same to the presidential palace in Cairo.
Clashes erupted on 5 December between supporters and opponents of Morsi at the presidential palace, where an opposition sit-in was being held against Egypt's draft constitution, which critics say is "unrepresentative" of Egyptian society. They assert that the document was drafted by an Islamist-led Constituent Assembly that saw walkouts by church representatives, liberals, leftists and other non-Islamist members.
Ten people – from both sides – were killed in the ensuing violence, with both sides trading accusations of responsibility for the bloodshed.
Shortly after 10pm local time, however, Abu-Ismail vehemently denied that his supporters had attacked Wafd Party headquarters.
"I know nothing about any riots or any attempts to lay siege to any headquarters. Blaming me for this is a media farce. It's obvious that the media is targeting me," the one-time presidential hopeful declared on his Facebook page.