They say the blast took place shortly before midnight on Wednesday and that the four killed included two policemen.
A Palestinian delegation including Hamas officials was due to arrive later on Saturday in Cairo for new talks.
An Egyptian foreign ministry official said he could not confirm or deny the new invitation.
The new prices were made public only a few hours before the decision was implemented.
The attack comes two days after gunmen attacked a military bus in the capital, killing a soldier.
Why most Egyptians want their charismatic army chief as president.
Egyptian citizen Ahmed Aleiba was detained by the Egyptian authorities in Cairo for three weeks without any charges.
The case is rooted in the 2011 escape of more than 20,000 inmates from Egyptian prisons, including Morsi.
Most of the deaths were in Cairo and its suburbs, and others in Alexandria and Minya, while 247 were injured, the health ministry said on Sunday.
More than 1,000 people,mostly Islamists,died in street
A keenly anticipated peace conference for Syria will convene in Geneva on November 23.
A policeman was killed in El-Arish in north Sinai,security and medical sources said.
Prime Minister Hazem Beblawi urged Egyptians to unite,saying the country is on the road to recovery.
Gehad el-Haddad,of the Muslim Brotherhood on Tuesday along with other senior members of the group.
Fawzi Barhoum says the allegation is an ‘attemp to demonize Hamas’.