KIRIYAT MALACHI, Israel -- Israeli tanks and troops moved Thursday night toward the Gaza Strip in apparent preparation for a possible invasion of the crowded seaside enclave after a day of violence that included two militant rocket strikes on the southern suburbs of Tel Aviv, raising the likelihood that the region was on the brink of all-out war.
A day after Israeli aircraft and warships retaliated for hundreds of rockets fired into the country in recent weeks by striking scores of targets in Gaza in the biggest Israeli military operation in four years, Israeli Defense Minister Ehud Barak summoned more than 30,000 reservists to military duty. Mr. Barak said the order was intended to make Israel "ready for any development."
Those soldiers could be seen from the Israeli city of Kiriyat Malachi, 20 miles north of Gaza, massing and heading toward the border, even as officials indicated that the decision to invade had not yet been made.
"We have made the preparations, and entering is certainly an option," said a senior Israeli military official based in southern Israel, who spoke only on condition of anonymity under the military's ground rules. "If the politicians were looking for an excuse, Hamas gave them one."
That was a reference to rockets fired by militants in Gaza that struck neighborhoods across the southern Tel Aviv metropolis, the first time Palestinian rockets had reached the densely populated urban center where more than 40 percent of Israelis live.
No one was injured in the strikes on Tel Aviv, but three people died in Kiriyat Malachi when a militant's rocket struck a four-story building.
The possibility of all-out war alarmed countries across the globe. Egypt's Islamist government said Prime Minister Hesham Kandil would visit Gaza today in a show of solidarity with Hamas and ordered the border crossing at Rafah opened around the clock to allow wounded Gazans to seek medical care in Egypt. Gaza's Hamas leaders said offers of assistance were pouring in from throughout the Arab world.
The United States expressed support for Israel and blamed Hamas for triggering the violence by allowing militants to fire rockets into Israel. President Barack Obama spoke with Egypt's Islamist president, Mohammed Morsi, and urged him to broker a cease-fire. Hamas considers itself a close ally of Egypt's Muslim Brotherhood, of which Mr. Morsi was a leading member before he assumed the presidency.
France, too, sought to broker peace between the two sides, with the country's prime minister saying President Francois Hollande had been in touch with Israeli Prime Minister Benjamin Netanyahu and Mr. Morsi. The French prime minister, Jean-Marc Ayrault, called the violence "dangerous for the security" of both Israelis and Palestinians, according to news reports.
Mr. Morsi sided with Hamas, saying, "The Israelis must realize that this aggression is unacceptable and would only lead to instability in the region and would negatively and greatly impact the security of the region."
On the streets of Tel Aviv, there was a new sense of vulnerability, even though police said the two rockets that landed had done so harmlessly, one falling into the water just off the beach in the Tel Aviv neighborhood of Jaffa, and the other striking a field near the town of Rishon Lezion. Still, for many who had thought they lived in areas of the country safe from attack by Gaza militants, the sound of air raid warnings brought a new sense of dread.
Israelis strolling along Tel Aviv's beach promenade went sprawling into the sand in search of cover as police warned that they had fewer than 90 seconds from the sound of the first siren before a rocket was expected to land.
Police and military officials said they hadn't confirmed what type of rocket had managed to span the more then 40 miles between the Gaza Strip and the Tel Aviv area. But suspicion fell on Iranian-made Fajr missiles, which Israeli officials say Hamas militants have smuggled into Gaza in recent months. That prospect made it more likely that Israel would send troops into Gaza, as it became obvious that Israeli airstrikes on more than 70 missile-launching sites had failed to curb Hamas' ability to strike.
Hostilities between Israel and Gaza have increased steadily since Tuesday morning, when Israeli planes hit targets across Gaza and assassinated Hamas' top military leader, Ahmed Jabari. At least 15 people have died in Gaza since the bombing began, and hundreds have been wounded.