GAZA CITY (Ma'an) -- Israeli airforce planes flew over Gaza on Friday morning, dropping six shells on sites throughout the Strip, reportedly in retaliation for two projectiles launched from the coastal enclave earlier in the day.

An Israeli military spokeswoman said a "terror target" and two smuggling tunnels, in the north and southern Strip respectively, were the targets of the attacks.

Residents of Gaza city reported three explosions heard simultaneously at the Ansar government building west of Gaza city, a security center in the city's At-Tuffah neighborhood, and in an open area in the northern Gaza Strip in Bet Hannoun.

Israel's daily newspaper Haaretz cited Hamas sources claiming five were injured when Israeli fighter jest hit a training center in Gaza City.

Shortly after the Thursday night strikes, Israeli residents of the western Negev said an additional projectile landed in an open area, causing no injuries or damages.

As the strikes hit Gaza, Civil Defense vehicles headed toward the Ansar building, reporting heavy smoke emanating from the structure. Ma'an's correspondent said government security forces prohibited him and other journalists from accessing the site.

Shortly after the first set of strikes near Gaza city, witnesses said, Israeli war planes carried out three additional strikes on smuggling tunnels in the southern strip, damaging at lest two.

The military spokeswoman said the attacks were in response to "security-related incidents" which occurred throughout the previous week, and added that the military "holds Hamas solely responsible" for attacks on Israel.

No Gaza faction has claimed any of the three projectile launches reported by Israel over the previous three days.

*** An earlier version of this report said "terror tunnels" in the northern Strip were the target of Israeli strikes. An Israeli military spokeswoman later clarified that the site was a "terror target."