Two explosions were heard in Gaza City, one north of the city and one in the southern Gaza Strip town of Khan Yunis. Palestinian medics and witnesses said all the missiles appeared to land in open fields.
Two people, including a child, were lightly wounded, medics said.
An Israeli military spokesman said warplanes attacked two tunnels militants were digging in the direction of Israel, apparently to infiltrate the country and carry out attacks.
Israel routinely retaliates after rocket attacks from Gaza, and the latest air strikes came after a rocket hit the southern town of Netivot Thursday.
There were no casualties.
"We will not tolerate any attempt to disrupt the calm in Israel's southern communities," the spokesman said.
The conflict ended with mutual ceasefires on January 18 last year which have largely held despite violations by both sides.