JERUSALEM - When dusk descends on Jerusalem on a Friday, it usually brings a moment of rare harmony and almost magical tranquility. A steady siren announces the onset of the Jewish Sabbath just hours after Muslims wind up the special Friday noon prayer at al-Aqsa Mosque in the Old City.
So this Friday, when a rising-and-falling wartime siren wailed out at twilight, followed by at least two dull thuds, many did not immediately grasp what was happening.
In the 48 hours since Israel began its military operation against Gaza, militants' rocket attacks have extended farther and farther north, starting in southern Israel and advancing to Kiryat Malachi, then to Rishon Lezion and off the shore of Tel Aviv.
Throughout it all, residents of this disputed capital said they had felt largely immune from the battle by virtue of the city's religious sites and its huge Palestinian population. Until they heard the siren blaring.
"I thought 'Is that for Shabbat?'" recalled Judy Axelrod, a resident of predominantly Jewish West Jerusalem. When she realized it was not, she walked off into a YMCA for safety, even though most of those around her just carried on.
By firing at Jerusalem, about 48 miles from the Gaza border, Hamas had set a brazen precedent. The city was off-limits even to Saddam Hussein, the fallen Iraqi leader, when he fired Scud missiles at Israel during the first Persian Gulf War in 1991.
Israeli authorities did not immediately confirm the origin of the rocket fire, but it was assumed that the source was Gaza, where Hamas and its radical affiliates have amassed arsenals of smuggled rockets with increased ranges and more accurate trajectories in recent years.
On Thursday, they launched at least two at Tel Aviv, Israel's biggest city, and on Friday launched more as part of a response to a large-scale aerial assault by the Israelis on targets in Gaza and indications that Israel was close to launching its first ground invasion there in four years.
"We are sending a short and simple message: There is no security for any Zionist or any single inch of Palestine and we plan more surprises," Abu Obeida, a spokesman for the military of wing of Hamas, said in a message quoted by the Associated Press.
Israeli officials said the Iron Dome missile defense shield jointly developed with the United States is intercepting nearly 90 percent of Palestinian rockets that appear to be a threat to populated areas.
The Jerusalem rocket attack shattered plans for a temporary cease-fire during a remarkable visit to Gaza by the Egyptian prime minister that showed the shifting dynamics of Middle East politics since the turmoil of the Arab Spring uprisings.
The rocket fired at Tel Aviv on Friday probably landed in the sea, said a police spokesman, Micky Rosenfeld. Israeli officials say the only rockets in Gaza with a range that can reach Tel Aviv are the Iranian-made Fajr-5.
With a range of more than 50 miles, the Fajr-5 has changed the calculus of the conflict between Israel and Hamas, whose militants previously had been able to target only communities in Israel's sparsely populated south.
The rockets would have to have been smuggled by Hamas, which rejects Israel's right to exist. Israel continues to seal off its border with Gaza and blockades its seacoast for fear of weapons imports.
The fact that these rockets were still being fired seemed to weigh heavily in Israeli military calculations about a ground invasion. After a meeting with President Shimon Peres, Prime Minister Benjamin Netanyahu said that the Israeli army was "continuing to hit Hamas hard and is ready to expand the operation into Gaza," according to a statement from his office.
Netanyahu said that the aim was "to take out the terrorist infrastructure in Gaza while doing everything possible not to harm civilians."
The rapidly escalating confrontation between Hamas and Israel followed an Israeli airstrike on Wednesday that killed Hamas' top military commander.
Over the past three days, Israel has struck suspected rocket-launching sites and other Hamas targets in Gaza with scores of airstrikes, while Hamas has fired more than 450 rockets toward Israel. In all, 27 Palestinians and three Israelis have been killed.
On Friday, the Israeli army sent text messages to some 12,000 Gaza residents warning them to steer clear of Hamas operatives.
What sounded like airstrikes by Israeli F-16s were also audible in Gaza City. The Israeli military said no such strikes had taken place, but the Hamas Health Ministry reported that two people, including a child, were killed in the north of Gaza City while the Egyptian delegation was on the ground.
Witnesses on the Gaza-Israel border said Israeli tanks had massed in several places.
Early on Friday, the Israeli military said it had called up 16,000 army reservists after Defense Minister Ehud Barak authorized the call-up of 30,000.
President Barack Obama telephoned Netanyahu for the second time this week Friday, and officials at the White House, the Pentagon and the State Department have been on the phone with their Israeli counterparts since then.
During this call with Netanyahu, the White House said that Obama "reiterated U.S. support for Israel's right to defend itself, and expressed regret over the loss of Israeli and Palestinian civilian lives." The two leaders, the White House said, "discussed options for de-escalating the situation."
Information from the Associated Press and Washington Post was used in this report.
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1. Jerusalem: Rockets fired from the south fall short of the city.
2. Tel Aviv: Targeted again on Friday. The missile fell into the Mediterranean, officials said.
3. Kiryat Malachi: Three Israelis were killed in a rocket attack Thursday.
4. Gaza: Palestinian death toll rises to 27.