An Israeli police explosives expert holds the remains of a Gazan rocket after it landed in Kibbutz Nirim, outside southern Gaza. Baz Ratner / Reuters

An Israeli Iron Dome defense system missile intercepts a rocket fired from Gaza, July 8, 2014, one of scores aimed at Israeli towns in the past 24 hours. Abir Sultan / EPA

An explosion in Rafah in the southern Gaza Strip, July 8, 2014, after what police said was an Israeli airstrike — one of more than 100 on Monday and Tuesday. Ibraheem Abu Mustafa / Reuters

The Israeli army says it has continued to intensify its offensive on the Gaza Strip on Wednesday, 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.

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’s attacks on the Gaza Strip increased on Tuesday, with its military saying it launched more than a hundred airstrikes in 24 hours and mooting that the operation could become a longer-term military engagement with a possible ground component.

After the launch of airstrikes overnight on Tuesday, the Israeli government approved the call-up of up to 40,000 additional reservists, adding to the 1,500 already mobilized, the Israeli news outlet Haaretz reported.

The operation marks the worst outbreak of violence between Israel and Gaza since an eight-day war in 2012, and there was no indication that a lull in Israeli strikes would be forthcoming. At least 27 Palestinians have been killed in the latest round of bombardments with 130 more injured, according to Palestinian officials.

At least seven people were reportedly killed in an airstrike on a house in Khan Younis in Gaza, which injured 25 others. Local residents said the house belonged to the family of a Hamas member. After an initial strike on the house, dozens of people, including civilians, gathered on the roof, at which point, Reuters reported, the home was hit by another strike. The Israeli military had no comment on the attack.

Israel’s offensive, dubbed Operation Protective Edge, was said to be a response to a marked uptick in rocket attacks from Gaza, which on Monday reached their highest level in years. A representative for the Israeli military tweeted that Hamas has fired more than 130 rockets at Israel in the past 24 hours.

Fighters from Gaza managed to enter Israel from the sea and attacked several military sites simultaneously.

The Israeli army shot and killed four other Palestinians who were reportedly trying to infiltrate Zikim Kibbutz, an Israeli community near Gaza, Haaretz reported. Meanwhile clashes were also reported at a military base near Kerem Shalom as well as Yad Mordechai, according to Al Quds.

Sirens rang out over central Israel after rockets fired from Gaza traveled as far north as Haifa. Rockets were intercepted over Tel Aviv by Israel's Iron Dome, and at least one rocket exploded in Jerusalem, Haaretz reported.

Israeli Prime Minister Benjamin Netanyahu said Tuesday that the military operation against Hamas would be expanded — with the option of a ground invasion of Gaza.

A source in Netanyahu’s office quoted him as saying, “The IDF [Israel Defense Forces] must be ready to go all the way. All options are on the table, including a ground invasion.”

“We are preparing for a battle against Hamas, which will not end within a few days,” Israeli Defense Minister Moshe Yaalon said in a release.