Minutes after the Iranian-backed group confirmed the death of Bahaa Abu el-Atta, barrages of rockets were fired towards southern Israel from Gaza. Air-raid sirens sounded in Tel Aviv.
Palestinian militant group Islamic Jihad said one of its leaders was killed by Israeli forces in the Gaza Strip early Tuesday.
The group's armed wing confirmed the death in a statement after Israel said it had targeted Bahaa Abu el-Atta, 42, in a strike.
Islamic Jihad said the commander was conducting "a heroic act" at the time of his assassination and vowed revenge as a result.
It added that el-Atta's wife was also killed. Islamic Jihad is an Iranian-backed group that often carries out attacks independent of Hamas, the larger militant outfit that controls Gaza.
The Israel Defence Forces (IDF) said on Twitter: "We just targeted Islamic Jihad commander in Gaza, Baha Abu el-Atta."
"(He) was directly responsible for hundreds of terror attacks against Israeli civilians and soldiers," and "his next attack was imminent."
In another air raid later on Tuesday morning, an Islamic Jihad militant was killed in the Gaza Strip while riding a motorcycle. The Israeli military said he had been about to launch a rocket from the bike.
The Palestinian Health Ministry confirmed that three people had been killed and 18 other injured in total.
The airstrikes came days after the appointment of hard-line politician Naftali Bennett as Israel's defense minister. Bennett has long advocated tougher action against Palestinian militants.
But Jonathan Conricus, a military spokesperson, said the operation had been planned long ago.
Shortly after the strike, Palestinian militants launched a salvo of rockets into Israel. Air raid sirens continued to go off throughout the morning as far away as Holon and Rishon LeZion, two suburbs of Tel Aviv. The IDF said Islamic Jihad was "firing rockets indiscriminately at civilians across Israel."
A rocket fired from Gaza slammed into a major junction in southern Israel, narrowly missing two cars. One of the two drivers was taken to hospital with shrapnel wounds, the Magen David Adom (MDA) ambulance service confirmed. An 8-year-old Israeli girl suffered a cardiac arrest while running to a shelter in Holon, the MDA added.
Israel's Iron Dome aerial defense system shot down about 20 of 50 rockets fired from the Gaza Strip, an IDF statement said.
Israel shut down crossing points into Gaza and reduced the permissible fishing area off the territory's coast to 6 nautical miles in anticipation of a looming confrontation. Schools were also closed in communities and towns along the Gaza Strip's boundary and all the way to Tel Aviv, about 90 kilometers north of Gaza.
In a separate incident, Israel is reported to have struck a residential building in Syria's capital Damascus housing a commander of the Palestinian Islamic Jihad with two missiles, killing two people.
Syria's state-run news agency SANA said six people were killed in the early morning attack on Tuesday. A third missile landed in Daraya, a suburb of the capital, SANA said. It was not immediately clear if the Islamic Jihad commander, identified as Akram al-Ajouri, was among those killed in the attack.