GAZA -- Israeli war jets struck with air-to-ground missiles early Thursday military facilities in the Gaza Strip in response to earlier rockets firing from the enclave into Israel, witnesses and security officials said.

The war jets had first intensively hovered over Gaza before firing a missile, where a huge explosion was heard in the northwest part of Gaza city, said residents in the area.

Witnesses said that the war jets kept hovering over the Gaza Strip, where several explosions were heard in its northern, central and southern areas. Firefighting and ambulances rushed to the targeted areas.

Paramedics said no injuries were reported, while police and security forces evacuated buildings and security headquarters all over Gaza in fear of being targeted by Israel.

Security officials said that at least one missile was fired at a training facility that belongs to the Islamic Hamas movement' armed wing, known as al-Qassam Brigades. Huge explosion was heard in the area and no injuries were reported.

The Israeli airstrike was a response to an earlier rockets' attack on Israel carried out from northern Gaza city. Israel said three rockets were fired into Israel, but caused no damages or injuries.

However, Palestinian sources, speaking on condition of anonymity, said that a radical Islamic Salafist group, affiliated with the Islamic State (IS) organization was responsible for firing the rockets into Israel.

The Israeli media had earlier reported that the Salafists fired rockets into Israel due to deep differences with Hamas movement following Hamas crackdown on the group and the killing of one of its members on Tuesday.

It is the second time in one week that this group fired rockets from the Gaza Strip into Israel. Last week, Israeli war jets carried out six airstrikes on Hamas and Islamic Jihad military facilities in response to rockets firing.

On Tuesday, a Salafist group, affiliated with the (IS), claimed responsibility for the rockets, which were fired from Gaza into Israel. It said in a video tape that it is not committed to any truce with Israel.

The group also claimed responsibility for the rockets attack and gave Hamas a 48-hour ultimatum to stop its crackdown on its militants and bring them back all the weapons Hamas had confiscated from them.

The airstrikes on Gaza last week and early on Thursday have been the most intensive ones since the end of a large-scale Israeli military operation on the Gaza Strip that lasted for 50 days and ended on Aug. 26.