GAZA CITY, Gaza Strip -- Israel on Wednesday launched one of the most ferocious Gaza assaults since its invasion four years ago, hitting at least 20 targets in aerial attacks that killed the top Hamas military commander, drew strong Egyptian condemnation and escalated risks of a new Middle East war.
The Israelis coupled the airstrikes' intensity with the threat of another ground invasion and warnings to all Hamas leaders in Gaza to stay out of sight or risk the same fate as the Hamas military commander, Ahmed al-Jabari, who was killed in a pinpoint airstrike as he was traveling by car down a Gaza street.
"We recommend that no Hamas operatives, whether low-level or senior leaders, show their faces above ground in the days ahead," the Israel Defense Forces said in a Twitter message.
The ferocity of the airstrikes, which Israel called Operation "Pillar of Defense" in response to repeated rocket attacks by Gaza-based Palestinian militants, provoked rage in Gaza, where Hamas said the strikes amounted to war and promised a harsh response. Israeli civil defense authorities raised alert levels and told residents to take precautions for rocket retaliation from Gaza.
Health officials in Gaza quoted by news agencies said the Israeli attacks had killed at least nine people and wounded at least 40.
The abrupt escalation in hostilities between Israel and Hamas, the militant organization Israel regards as a terrorist group sworn to its destruction, came amid rising tensions between Israel and all of its Arab neighbors. Israel has faced growing lawlessness on its border with the Sinai, including cross-border attacks. It recently fired twice into Syria, which is caught in a civil war, after munitions fell in the Israeli-occupied Golan Heights, and it has absorbed rocket fire from Gaza, which has damaged homes and frightened the population.
Israeli officials had promised a robust response to the rocket fire but for the moment, at least, opted against a ground invasion and instead chose airstrikes and targeted killings.
The Israeli attacks especially threatened to further complicate Israel's fragile relations with Egypt, where the Islamist-led government of President Mohammed Morsi, reversing a policy of ousted predecessor Hosni Mubarak, had established closer ties with Hamas and had been acting as a mediator to restore calm between Israel and Gaza-based militant groups.
In the first crisis in Israeli-Egyptian relations since Mr. Morsi came to power, he called the Israeli actions "wanton aggression on the Gaza Strip." He ordered Egypt's ambassador to Israel to return home, summoned the Israeli ambassador to protest and called for emergency meetings of both the U.N. Security Council and the Arab League over the Gaza attacks. Egyptian state media said Foreign Minister Mohamed Amr had "warned Israel against the consequences of escalation and the negative reflections it may have on the security and stability of the region."
Mr. Morsi's Freedom and Justice Party, founded by the Muslim Brotherhood, issued a statement saying: "The wanton aggression against Gaza proves that Israel has yet to realize that Egypt has changed, and that the Egyptian people who revolted against oppression will not accept assaulting Gaza."
Hamas spokesman Fawzi Barhoum said the Israelis had "committed a dangerous crime and broke all red lines," and that "the Israeli occupation will regret and pay a high price."
Military officials in Israel, which announced responsibility for Mr. Jabari's death, later said in a statement that their forces had carried out additional airstrikes in Gaza targeting what they described as "a significant number of long-range rocket sites" owned by Hamas that had stored rockets capable of reaching 25 miles into Israel. The statement said the airstrikes had dealt a "significant blow to the terror organization's underground rocket-launching capabilities."
Hamas and Gaza medical officials said both Mr. Jabari and a companion were killed by the airstrike on his car in Gaza City. Israeli media said the companion was Mr. Jabari's son, but there was no immediate confirmation.
The Israel Defense Forces said in a statement that Mr. Jabari had been targeted because he "served in the upper echelon of the Hamas command and was directly responsible for executing terror attacks against the state of Israel in the past number of years," including the 2006 abduction and five-year incarceration of Israeli soldier Gilad Shalit on the Israel-Gaza border.
The statement said the attack's purpose was to "severely impair the command-and-control chain of the Hamas leadership as well as its terrorist infrastructure." The statement did not specify how the Israelis knew Mr. Jabari was in the car, but said the operation had been "implemented on the basis of concrete intelligence and using advanced capabilities."
The Israel Defense Forces posted a YouTube video showing an aerial view of the attack on what it identified as Mr. Jabari's car on a Gaza street as it was targeted and instantly blown up in a pinpoint bombing. News photographs showed the car's blackened hulk surrounded by a large crowd. Later, the Israel Defense Forces posted on Twitter a Jabari mugshot overwritten with the word "eliminated."
Hamas has controlled Gaza since 2007, a year after the Israelis withdrew from territory captured in the 1967 Arab-Israeli war. But Israeli forces went back into Gaza in the 2008-09 winter in response to what they called a terrorist campaign by Palestinian militants there to launch rockets into Israel. The three-week military campaign killed as many as 1,400 Palestinians, including hundreds of civilians, and was widely condemned internationally.
Since then, Hamas has mostly adhered to an informal, if shaky, cease-fire and at times tried to force smaller militant groups to stick to it. But in recent months, pressured by some Gazans for not avenging Israel's deadly airstrikes, it has claimed responsibility for participating in rocket firings. Last week, it also claimed credit for detonating a tunnel packed with explosives along the Israel-Gaza border as Israeli soldiers were working nearby.
Israel has mainly responded to rocket attacks in recent years by attacking rocket-launching squads, empty training sites or arms manufacturing plants. Israel also had not attempted high-profile assassinations, but it has killed local leaders of small, radical Islamic groups it said were involved in planning attacks on Israelis.