Supporters of the ousted Egyptian President Mohammed Morsi say the security forces have begun operations to clear their two huge sit-ins in Cairo. The BBC's James Reynolds has seen an armoured bulldozer heading towards barricades protecting one of the protest camps outside the Rabaa al-Adawiya mosque, in the north-east of the capital. He says he can hear bursts of gunfire, a nearby side street has been blocked off, and plumes of black smoke can be seen in the distance.
A security tells the AFP news agency: "It is the beginning of the operation to disperse the protesters."
Al-Arabiya TV is broadcasting images of clouds of tear gas, collapsed tents and tires burning at the Rabaa al-Adawiya protest site.
There are already unconfirmed reports of at least five deaths at Rabaa al-Adawiya. The Reuters news agency is quoting an eyewitness as saying that 15 have been killed.
Security officials say tear gas has been fired into the larger of the two protest camps outside the Rabaa al-Adawiya mosque. At Nahda Square, armoured vehicles have been seen securing the area.
Egypt's interior ministry has issued a statement saying: "Upon the government's assignment to take necessary measures against the Rabaa and Nahda sit-ins, and out of national responsibility to protect citizens' security, the security forces have started to take necessary measures to disperse both sit-ins. It will provide safe exit for protesters and will not pursue them, except those who are wanted by prosecutors. The ministry is keen not to shed any Egyptian blood."
The main pro-Morsi protest camp is in a square near the Rabaa al-Adawiya mosque in the eastern district of Nasr City. You can view a clickable picture of the camp here.
Before the raid, at around 05:00 local time, the BBC's James Reynolds posted a photo on Twitter of the makeshift barricades outside the Rabaa al-Adawiya camp.