ASHKELON, Israel — Sarah Ziski and her two children hovered close to the bomb shelter outside their Ashkelon home, ready to dart inside at the first sound of an air raid siren.

For the last four days, the area around Ziski's home has been the target of frequent rocket attacks by militants in the Palestinian territory of Gaza. Along with about 1 million residents of southern Israel, she's fallen into the range of an extended arsenal of rockets and missiles. Life as they know it, she said, has effectively stopped.

"There is no school, no work. It feels like war to us," she said. "We don't know when it will start and when it will end."

The most recent exchange of violence between Israel and militants in Gaza began Friday, shattering a months-long calm. An Israeli airstrike carried out a "targeted killing" of Zuhair al Qaissi, a senior member of the Popular Resistance Committee, an umbrella group that includes militants from various Palestinian factions.

Israel's military said Qaissi was the mastermind behind cross-border attacks on Israel through its southern border with Egypt and that he was planning an imminent attack. A drone strike hit a car he was traveling in, and he died instantly. Within hours, rocket barrages began hitting southern Israel.

In response, Israel has continued airstrikes on what it says are militant targets, including rocket-launching sites. In four days of Israeli strikes, at least 21 Palestinians have been killed, three of them civilians. Dozens more have been wounded, according to Palestinian medics in Gaza.

Israeli officials said hundreds of rockets had been fired at southern Israel, though the country's missile interceptor system has shot down more than 90 percent of the rockets aimed at Israel.

Israeli officials said Monday that the violence could continue for days, or until they significantly damaged the infrastructure of militant groups in Gaza. They cited intelligence saying Qaissi was planning an imminent attack and said officials "at the highest echelons" had signed off on the killing.

"It was a clear and right decision," said Brig. Gen. Yoav Mordechai, a spokesman for the Israel Defense Forces.

But for many Israelis affected by the current round of violence, the decision has raised questions over how high a toll they'll pay.

"I don't know, I trust the army, but was it worth it to kill this one guy? To have all of us in the south suffer and put our lives in danger and have everything sparked up again? I just don't know," Ziski said.

Israel's policy of "targeted killing" for militants in the Palestinian territories has been in place since the early 2000s. Sanctioned at the highest levels of the government and military, it began as a way to eliminate targets that the military felt it couldn't detain or arrest. It's been used most widely in the Gaza Strip, particularly after Israel withdrew from the coastal territory in 2005.

The country first employed the tactic "in instances when Israel could not physically reach the target and apprehend him or her without minimum collateral damage," said Yaakov Katz, a military analyst and the author of "Israel vs. Iran: The Shadow War."

"What started with large-scale bombings has been perfected over the years with the use of surgical, accurate weapons that rarely cause civilian casualties."