Israeli leaders have threatened to widen the operation if the rocket fire doesn't halt. Foreign Minister Avigdor Lieberman said options included the possible assassination of Hamas' prime minister, Ismail Haniyeh, and other top leaders.
"Every time that Hamas fires, there will be a more and more severe response," he told Channel 2 TV. "I really recommend all the Hamas leadership in Gaza not to try us again. . . . Nobody is immune there, not Haniyeh and not anybody else."
While Israeli military officials insist they have inflicted heavy damage on Hamas, there has been no halt to the militants' rocket fire. Hundreds of rockets have been fired, including a number of sophisticated weapons never before used.
The rocket attack on Jerusalem was unprecedented, setting off the eerie wail of air raid sirens across the city shortly after the beginning of the Jewish sabbath, a time when roads are empty. Police said the rocket landed in an open area southeast of the city. Earlier Friday, Hamas fired a rocket at Tel Aviv that also landed in an open area.
Israel's two largest cities have never before been exposed to rocket fire from Gaza.
Over the last three days, Israel has hit suspected rocket-launching sites and other Hamas targets in Gaza with scores of air strikes, 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 about 12,000 Gaza residents warning them to steer clear of Hamas operatives.
An attack on Jerusalem, claimed by both Israel and the Palestinians as their capital, was especially bold, both for its symbolism and its distance from the Palestinian territory. Located roughly 50 miles from the Gaza border, Jerusalem had been thought to be beyond the range of Gaza rockets.
"We are sending a short and simple message: There is no security for any Zionist on any single inch of Palestine, and we plan more surprises," said Abu Obeida, a spokesman for Hamas' armed wing.
It marked a bit of a gamble for the militants. The rocket landed near the Palestinian city of Bethlehem and just a few miles from the revered Al-Aqsa Mosque in Jerusalem's Old City, one of Islam's holiest sites.
Hamas, an Iranian-backed group committed to Israel's destruction, was badly bruised during its last full-fledged confrontation with Israel four years ago that ended with an informal truce, although rocket fire and Israeli air strikes on militant operations continued sporadically.
Just a few years ago, Palestinian rockets were limited to crude, homemade devices manufactured in Gaza. But in recent years, Hamas and other armed groups have smuggled in sophisticated, longer-range rockets from Iran and Libya, which has been flush with weapons since Moammar Gadhafi was ousted last year.
Hamas said the rockets aimed at the two Israeli cities Friday were made in Gaza, a prototype the militants call M-75, and have a range of about 50 miles. The Israeli military also released a video of what it said was an attempt by Hamas to launch an unmanned drone aircraft. Neither weapon was previously known to be used by Hamas.
Israeli Prime Minister Benjamin Netanyahu huddled with his emergency cabinet Friday night. Israeli media reported that the meeting approved a request from Defense Minister Ehud Barak to draft 75,000 reservists. Earlier this week, the government approved a separate call-up of as many as 30,000 soldiers. Combined, it would be the biggest call-up of reserves in a decade.
Lt. Col. Avital Leibovich, a military spokeswoman, said that 16,000 reservists were called to duty Friday and that others could soon follow.
She said that no decision had been made on a ground offensive but that all options were on the table. Dozens of armored vehicles have been moved to Israel's border with Gaza since fighting intensified Wednesday.
In Washington, the White House said Netanyahu called President Obama on Friday to provide an update on the situation. Netanyahu expressed appreciation to Obama and the American people for U.S. investment in the Iron Dome rocket and mortar defense system, which has been used to defend Israel against rocket attacks from Gaza. The two leaders also spoke Wednesday.
Protesters in Center City respond to violence in Israel, Gaza. B1