The Israeli Air Force launched airstrikes in the Gaza Strip shortly after 10 p.m. on Wednesday in retaliation for a massive rocket barrage earlier in the day, the largest of its kind since 2012.

Israeli planes struck 29 targets in the Strip, the army said in a statement. Palestinians said at least five strategic points were hit in the coastal enclave, primarily in areas around the cities of Khan Younis and Rafah.

Israel had warned that it would hit back hard at Gaza terror groups, after more than 50 rockets were fired at southern Israel.

Among the IAF targets were bases of the armed wing of Islamic Jihad, which had claimed the rocket attacks, and Hamas throughout the Gaza Strip, Palestinian witnesses said. No Palestinian casualties were initially reported. Earlier, IDF tanks fired shells at targets in the Strip.

“All of our planes safely returned to their bases,” the IDF said in a statement. “The attack was carried out in retaliation for the massive ballistic bombardment of Israeli territory this evening. The IDF will not abide any attempt to harm Israeli civilians and IDF soldiers, and will continue to act decisively against anyone who employs terrorism against the State of Israel.”

Israeli military sources said after the late-night retaliatory strikes that Israel would now wait to see how Hamas and Islamic Jihad responded. If there were no further rocket attacks on Israel, the current flare-up would be over. But if there was more rocket fire, Israel would again respond.

As of late Wednesday night, the Israeli authorities had not canceled school for children in the south Thursday.

Although the rocket fire from Gaza subsided late in the evening, Israel raised its security alert in the south, and residents were told to stay within 15 seconds of rooms reinforced against rockets, amid indications that the dramatically escalated new round of confrontation was not over.

At least two rockets from Gaza fell in residential areas, one of them causing light damage in Sderot. There were no direct injuries, but a Sderot woman, aged 57, was lightly hurt as she ran for cover.

“If there is no quiet in our south, no quiet for the residents of Israel, there will be noise, lots of noise in Gaza,” Prime Minister Benjamin Netanyahu said at a joint press conference with his British counterpart, David Cameron. “And that’s putting it mildly.”

Cameron called the rocket strikes on Israel “barbaric.”

The US State Department decried the barrage of rockets from the Gaza Strip on Wednesday, referring to it as “reprehensible,” and stressing that Israel reserves the right to protect its citizens.

“The United States condemns in the strongest terms today’s rocket attacks into Israel by terrorists from the Gaza Strip,” read a statement from spokeswoman Jen Psaki.

“There is no justification for such attacks. We call for these terrorist attacks to cease immediately. Israel, like any nation, has a right to defend itself.”

The Islamic Jihad terror group took credit for the attacks — the worst since November 2012 — saying they were a retaliation for Israel’s killing of three of its operatives on Tuesday and that they signaled the start of an ongoing campaign.

Adiv Sterman and AFP contributed to this report.