GAZA CITY, Gaza Strip (AP) -- 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.