A bomb wounded three civilians, one of whom later died, when it exploded on the outskirts of Egypt's second city of Alexandria, police said.
A 12-year-old boy was among those hurt in the explosion near a residential neighbourhood on the western outskirts of the Mediterranean city.
Police said the blast had targeted a mobile checkpoint that had already been moved when the bomb exploded.
Earlier, a small bomb hidden in an electrical transformer exploded in central Cairo without causing any casualties.
The blast occurred on a street close to Tahrir Square -- the epicentre of the 2011 revolt that ousted long-time president Hosni Mubarak.
There were no immediate claims of responsiblity for the two explosions.
Signup to our newsletter and follow us on Facebook and Twitter!
Two "sound bombs" were also defused near a parking lot at Cairo International Airport, security officials said.
One of them was found in a gift bag outside Terminal Three. When airport security officials reported it to police the second device was discovered by sniffer dogs under a policeman's car outside the terminal.
Scores of policemen and soldiers have died in militant attacks, mostly in the Sinai Peninsula, since the army toppled Islamist president Mohamed Morsi in 2013.
The latest assault was in North Sinai Thursday, killing 30 soldiers and wounding scores of other people.
That attack with rocket fire and a suicide car bomb targeted a miliary base, a police headquarters and a residential complex housing army and police officers.
The militants say their attacks are to avenge a deadly crackdown on Morsi supporters since his overthrow.