GAZA - Israel launched three air strikes in the Gaza Strip on Thursday, witnesses and the Islamist group Hamas said, after a day in which about a dozen mortar bombs and rockets fired from the territory struck inside the Jewish state.

There were no immediate reports of casualties from the attacks in Gaza City and Khan Younis which caused explosions, and sent smoke and flames shooting into the air. There were also no casualties from the attacks on Israel.

The Israeli armed forces had no immediate comment.

The strike appeared to be Israel's first inside the crowded city of Gaza since a three-week offensive last January in which 1,400 Palestinians and 13 Israelis were killed.

Israeli media reports said Israel had targeted a weapons factory in Gaza City.

Hamas, an Islamic militant group that rules Gaza, said an Israeli warplane bombed a building in Gaza City that witnesses said appeared to belong to the Islamic Jihad militant group.

Militants barred reporters from reaching the area.

Israel later fired two missiles at targets in Khan Younis, a town in southern Gaza, witnesses said. At least one of the missiles struck in an uninhabited area near a school, and there were no immediate reports of casualties.

Israel earlier distributed leaflets in Gaza, warning many of its 1.5 million residents to avoid areas within 300 meters (yards) of the border fence with Israel.

The mortar bombs and rocket fired at Israel earlier on Thursday caused no casualties, an Israeli military spokesman said. The number of such attacks has been on the rise in the past few weeks after months of relative calm since the Gaza war.

(Writing by Allyn Fisher-Ilan)

Israel