GAZA CITY, Gaza Strip (AP) -- Palestinian militants took aim at Jerusalem for the first time Friday, launching a rocket attack on the holy city in a major escalation of hostilities as Israel pressed forward with a relentless campaign of airstrikes in the Gaza Strip.
Israel called up thousands of reservists and massed troops along the border with Gaza, signaling a ground invasion of the densely populated seaside strip could be imminent. The attack on Jerusalem, along with an earlier strike on the metropolis of Tel Aviv, raised the likelihood that Israel would soon move in.
Israel launched its military campaign Wednesday after days of heavy rocket fire from Gaza by assassinating the military chief of the territory's ruling Hamas militant group. Since then it has carried out hundreds of airstrikes on weapons-storage facilities and underground rocket-launching sites.
It has slowly expanded its operation beyond military targets and before dawn on Saturday, missiles smashed into a small Hamas security facility as well as the sprawling Hamas police headquarters in Gaza City, setting off a massive blaze there that threatened to engulf nearby houses and civilian cars parked outside. No one was inside the buildings at the time.
A separate airstrike leveled a mosque in central Gaza, damaging nearby houses, Gaza security officials and residents said. The military had no comment on that attack and it wasn't clear whether weapons or fighters were being harbored in the area.
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 on 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 Hamas-ruled Gaza.
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.
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 (80 kilometers) 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 airstrikes 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 (80.46 kilometers). 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 on Friday night. Israeli media reported 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 16,000 reservists were called to duty on Friday and others could soon follow.
She said no decision had been made on a ground offensive but all options are on the table. Dozens of armored vehicles have been moved to Israel's border with Gaza since fighting intensified Wednesday.
The violence has widened the instability gripping the region, straining already frayed Israel-Egypt relations. The Islamist government in Cairo, linked like Hamas to the region-wide Muslim Brotherhood, recalled its ambassador in protest and dispatched Prime Minister Hesham Kandil to show solidarity with Gaza.
Kandil called for an end to the offensive while touring Gaza City's Shifa Hospital with Haniyeh, the Gaza prime minister who was making his first public appearance since the fighting began.
In one chaotic moment, a man rushed toward the two leaders, shouting as he held up the body of a 4-year-old boy. The two prime ministers cradled the lifeless boy who Hamas said was killed in an Israeli airstrike. Israel vociferously denied the claim, saying it had not operated in the area.
Fighting to hold back tears, Kandil told reporters the Israeli operation must end.
"What I saw today in the hospital, the wounded and the martyrs, the boy ... whose blood is still on my hands and clothes, is something that we cannot keep silent about," he said.
An Egyptian intelligence official, meanwhile, said an Egyptian proposal for a cease-fire in Gaza was presented Friday to Haniyeh and other Hamas leaders. The details were not made public.
However, Hamas replied that a cease-fire was premature because military chief Ahmed Jaabari's "blood has not dried yet."
The Egyptian official said Hamas officials promised to study the cease-fire proposal again in the coming days. The official spoke on condition of anonymity because he was not authorized to release the information.
A senior Hamas official confirmed that Egypt, which often mediates between Hamas and Israel, was working behind the scenes to arrange a truce.
The official, speaking on condition of anonymity because he was discussing a sensitive diplomatic matter, said Hamas was demanding an end to the offensive, limits on Israeli ground activities along the border, a permanent halt in assassinations of Hamas leaders and an end to Israel's blockade of Gaza.
"These conditions must be honored and sponsored by a third party," he said. "We will stop all armed activities out of Gaza in return."
An Israeli official refused to say whether Egypt or any other country was involved in cease-fire efforts but said Israel would not settle for anything less than a complete and long-standing halt to the rocket fire. "We're not interested in a timeout that returns us to square one," he said, speaking on condition of anonymity because he was not allowed to discuss the matter with the media.
Federman reported from Jerusalem. Aya Batrawi in Cairo and Ian Deitch in Jerusalem contributed reporting.