(Corrects to say 6th of October City west of Cairo)
CAIRO, June 28 (Reuters) - Two bombs exploded at a small telephone exchange on Cairo's outskirts on Saturday, killing an 18-year-old woman and her mother, security sources said, days after a string of small bomb explosions hit the Egyptian capital's metro network.
Near Rafah in North Sinai, gunmen killed four Egyptian soldiers, state media and security sources said.
The gunmen forced the soldiers, who were returning from a holiday and dressed in civilian clothing, out of their vehicle and shot them before escaping, the state news agency MENA reported.
No group immediately claimed responsibility for either attack.
The exchange building was still under construction, and it appeared likely that the devices that exploded had been intended for use elsewhere, security sources and a judicial source said.
The unfinished concrete building partially collapsed in the blast. The two women killed were the wife and daughter of a construction site guard who lived in an annex to the building in 6th of October City, a western satellite district of Cairo.
Egypt has been hit by a wave of violence, mainly by militants based in the Sinai peninsula against security forces, since the army ousted President Mohamed Mursi of the Muslim Brotherhood last July.
On Wednesday, eight people were hurt in northern Cairo when homemade explosive devices blew up at four metro stations and a courthouse in the first attacks in Cairo since Abdel Fattah al-Sisi became president earlier this month.
The Interior Ministry said in a statement on Facebook that security forces and bomb experts were inspecting the site of the exchange blasts.
(Reporting By Shadia Nasralla and Reuters TV; Editing by Sophie Hares and Kevin Liffey)