JERUSALEM –  Israel expanded its air assault on rockets in the Gaza Strip on Saturday, striking a Hamas government compound and a Cabinet building where Gaza Prime Minister Ismail Haniyeh met with Egypt's prime minister on Friday.

Bombarding the Gaza Strip with nearly 200 airstrikes, the Israeli military targeted the militants' weapons-storage facilities and underground rocket-launching sites.

Israeli aircraft also bombed a police headquarters building in Gaza City, which set off a huge blaze that engulfed nearby houses and civilian cars parked outside, the Interior Ministry reported. No one was inside the buildings.

A three-story apartment building belonging to a Hamas military commander was also hit, and ambulances ferried out more than 30 inhabitants wounded by the powerful explosion.

Missiles knocked out five electricity transformers, plunging more than 400,000 people in southern Gaza into darkness, according to the Gaza electricity distribution company.

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 800 airstrikes since, the military said.

Gaza 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.

Two rockets landed in open fields outside of Jerusalem after air raid sirens sounded in the city Friday, sending Israelis running for cover. The strike marked the first time the holy city has been targeted by rockets fired by Gaza militants. There were no immediate reports of damage or causalities.

Israeli media say the rocket fell north of Jerusalem, as witnesses say they saw a stream of smoke in Mevasseret Zion, a suburb.

Israeli police spokeswoman Micky Rosenfeld said the rocket landed in an open area near Gush Ezion, a collection of Jewish settlements in the West Bank southeast of the city.

In Gaza, Hamas militants said they had attacked Jerusalem. The attack marks a major escalation, both for its symbolism and its distance from the Palestinian territory. Jerusalem had been thought to be beyond the range of Gaza rocket squads.

“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,” Abu Obeida, a spokesman for the Hamas militant wing said.

Militants already have fired rockets into the southern outskirts of Tel Aviv on Thursday. The rocket attacks have not hurt anyone, but have caused panic.

Lt. Col. Avital Leibovich, a military spokeswoman, said the Israeli military had called 16,000 reservists to duty on Friday as it geared up for a possible ground offensive.

She said the army had authority to draft an additional 14,000 soldiers. She would not say where the troops were deployed.

Ten people, including five militants, were killed and dozens were wounded in the various attacks Saturday, according to Gaza officials. In all, 40 Palestinians including 13 civilians and three Israeli civilians have been killed since the Israeli operation began.

Egypt's prime minister rushed to the aid of the Gaza Strip's Hamas rulers Friday in the midst of an Israeli offensive there, calling for an end to the operation, as Palestinian rocket squads aimed at Tel Aviv for a second straight day. The visit served as a boost of solidarity for the Hamas militants who have vowed to resist the Israeli offensive.

Hopes of even a brief cease-fire were dashed after both sides accused the other of violating a proposed cease-fire during a visit by the prime minister of Egypt to Gaza.

Israeli Prime Minister Benjamin Netanyahu had told Egypt that Israel was prepared to suspend its military offensive in the Gaza Strip during Prime Minister Hisham Kandil's three-hour visit there Friday.

However, Israel later said Hamas did not honor the deal, saying rockets fired from Gaza had hit several sites in southern Israel as Kandil was in the enclave.

Israel strongly denied it had carried out any attacks from the time Kandil entered Gaza, though Gaza militants claimed Israel had continued strikes during the visit.

Along the border Friday, Israeli tanks, armored vehicles and military bulldozers were parked in neat rows. Leibovich said all options are open, “including a ground operation.”

Netanyahu said the army was hitting Hamas hard with what he called surgical strikes, and warned of a "significant widening" of the Gaza operation. Israel will "continue to take whatever action is necessary to defend our people," said Netanyahu, who is up for re-election in January.

"We will continue the attacks and we will increase the attacks, and I believe we will obtain our objectives," said Lt. Gen. Benny Gantz, Israel's military chief.

An Israeli ground offensive could be costly to both sides. In the last Gaza war, Israel devastated large areas of the territory, setting back Hamas' fighting capabilities but also paying the price of increasing diplomatic isolation because of a civilian death toll numbering in the hundreds.

The current round of fighting is reminiscent of the first days of that three-week offensive against Hamas. Israel also caught Hamas off-guard then with a barrage of missile strikes and threatened to follow up with a ground offensive.
However, much has also changed since then.

Israel has improved its missile defense systems, but is facing a more heavily armed Hamas. Israel estimates militants possess 12,000 rockets, including more sophisticated weapons from Iran and from Libyan stockpiles plundered after the fall of Muammar Qaddafi's regime there last year.

Netanyahu, who has clashed even with his allies over the deadlock in Mideast peace efforts, appears to have less diplomatic leeway than his predecessor, Ehud Olmert, making a lengthy military offensive harder to sustain.

What's more, regional alignments have changed dramatically since the last Gaza war. Hamas has emerged from its political isolation as its parent movement, the region-wide Muslim Brotherhood, rose to power in several countries in the wake of last year's Arab uprisings, particularly in Egypt.

Egypt recalled its ambassador to protest the Israeli offensive and has ordered his prime minister to lead a senior delegation to Gaza on Friday in a show of support for Hamas.

At the same time, while relations with Israel have cooled since the toppling of longtime Egyptian leader Hosni Mubarak, Morsi has not brought a radical change in Egypt's policy toward Israel.

He has promised to abide by Egypt's 1979 peace deal with Israel and his government has continued contacts with Israel through its non-Brotherhood members.

The Associated Press and Reuters contributed to this report.