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.

Al-Qassam Brigades, the armed wing of Hamas, said on its website on Tuesday, “If the enemy does not stop its bombing of houses policy, we will expand range of firing.” The group said it has rockets capable of reaching as far north as Tel Aviv and Jerusalem.

“There are airstrikes near me right now and no one in the streets,” Hamas spokeswoman Isra Almodallal told Al Jazeera later Tuesday. “The situation is really scary, there are lots of injured ... at least 100.”

According to Haaretz, Hamas politician Ismail Ashkar said Tuesday, “There will be no respite from the fighting as long as the attacks on Palestinians in the Gaza Strip and West Bank continue.”

He said also that any halt to attacks was dependent upon the release of Palestinian prisoners freed as a part of the 2011 Gilad Shalit prisoner swap — dozens of whom were recently rearrested by Israel in its crackdown following the deaths of three Israeli teens, which Israel blamed on Hamas. The group has denied involvement in their abductions.

Ashkar said the other condition for peace was for Israel to end its blockade on Gaza, which has been in place since 2007 when Hamas took power in the occupied territory. Since then, Israel’s military has controlled all movements in and out, including borders, air space and the sea. 

Netanyahu did not put a time limit on the operation, but diplomatic officials said it could be “for a long time.” He said the notion that “quiet would be met with quiet” was no longer the governing principle with regard to Israel and the Gaza Strip, and that it was time to “take off the gloves” against Hamas. Palestinian President Mahmoud Abbas on Tuesday called on Israel to halt its latest attacks.

The Israeli military said that more than 100 rockets had been fired at Israel, representing a sharp increase in the attacks that had been on the wane in recent months. Flights in and out of Ben Gurion Airport in Tel Aviv have been diverted north because of rockets fired from Gaza, Haaretz reported.

Al-Quds Brigades, Islamic Jihad’s military wing, said it launched 60 rockets at Israel on Tuesday — targeting Beersheba, Ashkelon and Netivot.

“It is our right to defend our people who are going through this battle alone without Arab or Islamic support,” an Islamic Jihad spokesman told Maan. “We are in the middle of the battle supporting our people … and we are committed to protecting them.”

Hamas, though initially thought to be reluctant to launch rockets at Israel, has also claimed credit for some of the rockets. Seven Israelis were reportedly lightly wounded in Ashdod — and another wounded when he fell while running to a bomb shelter, with the rest suffering from shock, Haaretz reported.

The Gaza operation comes amid tensions that have boiled over since June 12, when three Israeli teenagers went missing in the West Bank. Hundreds of Hamas members in the West Bank were arrested in the crackdown, which came weeks after Hamas and Fatah had signed an agreement to form a technocratic unity government in the West Bank and Gaza with elections set for later in the year.

After the bodies of the three Israeli teens were found in the West Bank last week, a Palestinian teenager was abducted and burned to death by hard-line Israelis seeking revenge. Six Israelis were arrested in connection with the murder over the weekend and three reportedly confessed to the crime on Monday. The crime set off massive street protests in East Jerusalem that pitted Palestinian youths against Israeli security forces.

Late Monday, according to Maan, an Israeli settler from the Nof Zion settlement in East Jerusalem reportedly opened fire on a group of Palestinian youths in front of a grocery store, but no injuries were reported and Israeli police gave no comment on the matter.

With wire services