Story by the Associated Press; curated by Oliver Darcy.

JERUSALEM (AP) — The Israeli army says it has intensified its offensive on the Hamas-ruled Gaza Strip, striking key Hamas sites in the second day of an operation aimed at quelling rocket fire against Israel.

Army spokesman Lt. Col. Peter Lerner says warplanes early Wednesday attacked more than 130 sites including Hamas command centers and rocket launchers.

Lerner says at least four rockets were fired at Israel overnight, a decline from the large barrage the evening before. Air raid sirens wailed in Tel Aviv and southern Israel early Wednesday.

An Iron Dome missile flies to intercept a rocket on July 8, 2014, in Ashdod, Israel. Due to recent escalation in the region, the Israeli army has started new deployments at the border with the Gaza Strip. In the past 3 weeks more than 130 rockets where reportedly fired from Gaza into Israel. (Ilia Yefimovich/Getty Images)

Gaza health official Ashraf Al-Kedra says overnight airstrikes killed one militant in south Gaza and an Islamic Jihad operative and five relatives in northern Gaza.

Israel is mobilizing troops for a possible ground invasion of the Palestinian territory to stop the rocket fire.