Egypt's military arrested a BBC journalist when it cleared out a central Cairo protest that left several protesters injured and dozens detained, officials with the British broadcaster said on Tuesday.

Shaimaa Khalil was detained on Monday after the military, backed by riot police, cleared the three-week sit-in in Tahrir Square, they said.

The BBC's foreign editor John Williams wrote on his Twitter account that the broadcaster was trying to secure her release.

"Very concerned at the detention of Shaimaa Khalil in Cairo -- a good journalist doing her job. Doing all we can to secure her release," he wrote.

Khalil had been posting updates on Twitter before her arrest.

""Careful!' someone just told me. 'They arrest anyone taking photos," she wrote.

Witnesses said soldiers and police beat demonstrators and broke mobile phones, targeting anyone taking pictures.

The legal rights group the Front for Defending Protester Detainees in Egypt said that more than 80 people were arrested.

The protesters in Tahrir had refused to end their sit-in after political factions withdrew for the Muslim holy month of Ramadan, which started in Egypt on Tuesday.