JERUSALEM -- Israeli aircraft and warships struck dozens of targets across the Gaza Strip on Wednesday in the opening hours of what military officials in Jerusalem said could be a days-long military operation. The attacks left at least one senior Hamas leader dead and terrorized tens of thousands of Gaza residents in the strip’s densely populated urban centers.

Palestinian medics reported that at least seven people had been killed and more than 20 wounded in airstrikes. Medics at Gaza’s Shifa Hospital identified one of those killed as a 5-year-old girl.

“We don’t know where to run. Every neighborhood is being hit now, every area,” Mazar Abu Hizma, a 31-year-old father of two, told McClatchy by phone. “My children are crying, my wife is crying, but we don’t know where to run. We don’t know where is safe.”

Dubbed Operation Pillar of Defense, the assault was the toughest Israeli military action in Gaza in four years. Israeli military officials said the campaign could continue for “days or longer.”

The assault drew international reaction, with Egypt recalling its ambassador to Israel in protest, while the United States blamed Hamas for triggering the violence and backed Israel.

“We support Israel’s right to defend itself, and we encourage Israel to continue to take every effort to avoid civilian casualties,” State Department spokesman Mark Toner said in a statement.

There were concerns that the violence could spiral, with Israel facing renewed threats on its northern and southern borders. Militants in Egypt’s Sinai Peninsula fired several rockets into Israel on Wednesday morning. Earlier this week, Syrian mortar fire landed in Israel, leading Israel to retaliate and hit a Syrian army post.

Israeli officials didn’t divulge the campaign’s precise goals, but their comments suggested that Israel intended to weaken Hamas, whose Gaza government has been receiving wider recognition recently, including an unprecedented visit last month by the emir of Qatar.

“We need to solve the ‘Hamas problem’ in Gaza,” said a senior official of the Israel Defense Forces in southern Israel, who spoke only on the condition of anonymity under the military’s ground rules.

The opening shots of the new campaign targeted Ahmed Jabari, the leader of Hamas’ military wing. He was killed while he was traveling with his bodyguard in a gray Kia Cerato on a narrow street in Gaza City. Within the hour, at least four other targets in Gaza were hit.

Militants in Gaza vowed to retaliate with volleys of missiles, prompting Israeli officials to close schools and public offices in southern Israel indefinitely and to urge civilians to stay close to bomb shelters. Residents of southern Israeli cities reported that air raid sirens could be heard late into the night. At least one volley of missiles was fired in the direction of Dimona, the site of one of Israel’s nuclear reactors.

“We will continue to strike in Gaza until our goals are met,” IDF spokesman Yuval Mordechai said. “We foresee protracted days of fighting.”

For civilians in the Gaza Strip and southern Israel, the sudden assault bore an unnerving resemblance to Operation Cast Lead, a punishing Israeli offensive into Gaza four years ago that saw thousands of rockets slam into southern Israeli communities, while Israeli airstrikes rocked the Gaza Strip. The three-week-long operation cost the lives of more than 1,300 Palestinians and 13 Israelis.