The Muslim Brotherhood urged Egyptians to take to the streets to "stop a massacre" after 17 people were killed on Wednesday as police moved in on two Islamist protest camps.

"This is not an attempt to disperse, but a bloody attempt to crush all voices of opposition to the military coup," Brotherhood spokesman Gehad al-Haddad said on Twitter.

The organisers of a protest at Rabaa al-Adawiya, where several Brotherhood leaders are staying, "is calling on Egyptians to take to the streets to stop the massacre," Haddad said.