Two bombings on Saturday in a Cairo suburb killed a teenager and her mother, officials said, the latest in a wave of blasts to hit the Egyptian capital this week.
Militants have stepped up attacks after the army ousted Islamist president Mohamed Morsi in July 2013 and amid a deadly crackdown by authorities on his supporters.
The makeshift bombs planted in a telecommunications being built in the October 6 suburb were detonated by a mobile phone signal at around 9:00 am (0700 GMT), a police investigator told AFP.
Medics said the watchman’s wife and 18-year-old daughter were killed.
Residents said the powerful blast rattled windows in nearby buildings.
Saturday’s explosion comes after five makeshift bombs at four Cairo metro stations on Wednesday and a sixth at a courthouse wounded six people.
The authorities have blamed Morsi’s Muslim Brotherhood for attacks rocking the country, most of which have targeted security forces, and have blacklisted the Islamist movement as a terrorist organisation.
Since Morsi’s ouster, a crackdown on his supporters has left more than 1,400 people dead and seen at least 15,000 jailed.
Hundreds have also been sentenced to death.
An Al-Qaeda-inspired jihadist group based in the Sinai Peninsula, Ansar Beit al-Maqdis (Partisans of Jerusalem), has claimed some of the deadliest attacks on security forces, as well as a failed attempt to assassinate the interior minister in September.
A little-known jihadist group, Ajnad Misr (Soldiers of Egypt), has also said it was behind a string of attacks on police in Cairo.
The government says the militants have killed about 500 people, most of them security personnel.