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.
An Israeli military spokesman said warplanes had 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 on Thursday without causing damage or casualties.
"We will not tolerate any attempt to disrupt the calm in Israel's southern communities," the spokesman said.
It marked the latest violence along Gaza's border, which has been mostly quiet since a war Israel launched on the strip on Dec. 27, 2008 that left more than 1,500 Palestinians dead and practically destroyed the strip's infrastructure.