GAZA CITY, Gaza Strip —  Israel expanded its fierce air assault on rocket operations in the Hamas-ruled Gaza Strip on Saturday, striking security compounds, smuggling tunnels and a three-story apartment building after an unprecedented rocket attack aimed at the holy city of Jerusalem raised the stakes in its confrontation with Palestinian militants.

Israeli aircraft also kept pounding their original targets, the militants’ weapons-storage facilities and underground rocket-launching sites. The Israeli military called up thousands of reservists and massed troops, tanks and armored vehicles along the border with Gaza, signaling a ground invasion of the densely populated seaside strip could be imminent.

Israel launched its military campaign Wednesday after days of heavy rocket fire from Gaza and has carried out some 700 airstrikes since, the military said. Militants, undaunted by the heavy damage the air attacks have inflicted, have unleashed some 500 rockets against the Jewish state, including new, longer-range weapons turned for the first time this week against Jerusalem and Israel’s Tel Aviv heartland.

Israel has slowly expanded its operation beyond military targets and before dawn on Saturday, the Gaza Interior Ministry reported, missiles smashed into two small Hamas security facilities as well as the massive Hamas police headquarters in Gaza City, setting off a huge blaze that engulfed nearby houses and civilian cars parked outside. No one was inside the buildings at the time.

The Interior Ministry said a government compound was also hit as devout Muslims streamed to the area for early morning prayers. So, too, was a Cabinet building where the Hamas prime minister received the prime minister of Egypt on Friday.

In southern Gaza, Israeli aircraft went after the hundreds of underground tunnels militants used to smuggle in weapons and other contraband from Egypt, people in the area reported. A huge explosion in the area sent buildings shuddering in the Egyptian city of El-Arish, 30 miles (45 kilometers) away, an Associated Press correspondent there reported. The tunnels have also been a lifeline for residents of the area during the recent fighting, providing a conduit for food, fuel and other goods after supplies stopped coming in from Israel days before the military operation began.

Missiles also knocked out five electricity transformers, plunging more than 400,000 people in southern Gaza into darkness, according to the Gaza electricity distribution company. A three-story apartment building belonging to a Hamas military commander was hit, and ambulances ferried out inhabitants wounded by the powerful explosion. Others were thought to be buried under the rubble.  

A mosque in central Gaza was also targeted, but it wasn’t clear whether weapons or fighters were being harbored in the area.

At least one person was killed and dozens were wounded in the various attacks, Gaza health official Ashraf al-Kidra said. In all, at least 30 Palestinians, including a dozen civilians, and three Israeli civilians have been killed since the Israeli operation began.

The Israeli military said it did not immediately have an accounting of its various overnight targets.

“The Palestinian government emphasizes its steadfastness and support for the Palestinian resistance,” government spokesman Ihab Hussein said in a text message to reporters after the wave of Israeli attacks. “It stands alongside its people, who are subject to this aggression.”

The widened scope of targets brings the two sides closer to the kind of all-out war they waged four years ago. Hamas, a group committed to Israel’s destruction, was badly bruised during that confrontation, but has since restocked its arsenal with more and better weapons, and has been under pressure from smaller, more militant groups to prove its commitment to armed struggle against Israel.

The attack aimed at Jerusalem on Friday and strikes on the Tel Aviv area twice this week dramatically showcased the militants’ new capabilities, including a locally made rocket that appears to have taken Israeli defense officials by surprise.  Both areas had remained outside the gunmen’s reach in past rounds of fighting, and their use dramatically escalated the hostilities.

Just a few years ago, Palestinian rockets were limited to crude devices manufactured in Gaza. But in recent years, Israeli officials say, 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.

The eerie wail of air raid sirens sounded in Jerusalem after the start of the Jewish Sabbath in the holy city, claimed by both Israel and the Palestinians as a capital and located about 75 kilometers (47 miles) from Gaza. Jerusalem residents were shocked to find themselves suddenly threatened by rocket fire, which, for more than a decade, had been limited to steadily broadening sections of southern Israel.

The attack on the contested city was especially audacious, both for its symbolism and its distance from Gaza. Located roughly 50 miles (80 kilometers) from the Gaza border, Jerusalem had been considered  beyond the range of Gaza rockets — and an unlikely target because it is home to the Al-Aqsa Mosque compound, Islam’s third-holiest shrine.

Most of the militants’ rockets do not have guided systems, limiting their accuracy, though Israeli officials believe the militants may have a small number of guided missiles that have not yet been used.

Israeli police spokesman Micky Rosenfeld said the rocket landed in an open area southeast of the city — near the Palestinian city of Bethlehem and just a few miles from Al-Aqsa.

Earlier on Friday, Gaza gunmen fired toward Tel Aviv for the second straight day, causing no injuries.

“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.

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 on Friday. “I really recommend all the Hamas leadership in Gaza not to try us again. ... Nobody is immune there, not Haniyeh and not anybody else.”

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 ose areas.   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 the territory on Friday to show solidarity.

President Barack Obama spoke separately to Israeli and Egyptian leaders Friday night as the violence in Gaza escalated. In a conversation with Israeli Prime Minister Benjamin Netanyahu, the American president reiterated U.S. support for Israel’s right to self-defense and discussed possible ways to scale back the conflict, the White House said, without offering specifics. Separately, Obama called Egyptian President Mohammed Morsi to praise Egypt’s efforts to ease tensions in the region.

At the same time, the changes in the region have opened up new possibilities for Hamas, by strengthening Islamists across the Middle East and bringing newfound recognition to the militant group shunned by the international community because of its refusal to renounce violence against Israel.

Last month’s landmark visit by Qatar’s emir and Friday’s solidarity mission by the Egyptian prime minister illustrated the growing acceptance of Hamas. The foreign minister of Tunisia is due to arrive in Gaza on Saturday, and Morocco’s foreign minister is to come Sunday. Neither country had dispatched representatives since Hamas violently overran Gaza in June 2007.