The Israeli cabinet on Friday evening okayed the military's request to expand the enlistment of reserve troops to 75,000, fueling speculation that a ground offensive in the Gaza Strip is imminent.

On Friday morning, army chief Lt. Gen. Benny Gantz issued call- up orders to 16,000 reservists, just over half of the 30,000 initially requested by Defense Minister Ehud Barak and authorized by cabinet ministers the previous day.

"We're going to significantly aggravate the operation," an official, speaking on condition of anonymity, told the Ynet news site.

The Defense Ministry in Tel Aviv neither confirmed nor denied that troop concentrations along the border with Gaza will be dramatically bolstered in the coming days.

"The defense minister authorized the Israel Defense Forces to expand its quota of reservists beyond the amount that was originally allocated. The request was submitted to the government for approval," the ministry said in a brief statement released late Friday night.

Most of the reservists already mobilized serve in Engineering Corps units which are considered vital for ground operations. Others include former members of Special Forces, paramedics, field intelligence officers, and combat-support and logistics personnel drafted via so-called No. 8 orders employed by the military in times of emergency.

Armored brigades, artillery and infantry battalions are already deployed along the Israeli side of the border. Major traffic arteries in the area were clogged with convoys of tanks, armored personnel carriers and trucks ferrying ammunition, water, fuel and other critical supplies to forces on stand-by.

The mass mobilization comes amid a sharp spike in cross-border violence that erupted Wednesday, when Israel launched an operation, code-named "Pillar of Defense," which aims to root out Hamas and other militant groups that intermittently fire rockets at southern Israel.

Some 550 rockets and mortars have slammed into Israel in the 72 hours since Israeli aircraft targeted Hamas military chief Ahmed Jabari in Gaza on Wednesday afternoon, prompting the organization to "declare war" on Israel.

Three Israelis were killed Thursday morning when a rocket hit an apartment building in the southern town of Kiryat Malachi.

After a relatively calm night on the Israeli side of the border, Friday morning saw the renewal of rocket fire from Gaza, with Hamas lobbing more than 60 projectiles at Ashdod, Asheklon, Be'er Sheva and other towns and villages in a roughly 30-kilometer arc around the coastal territory.

There were no reports of injuries, but homes and vehicles sustained damages, while dozens suffered shock, Israel Radio reported.

On Friday evening, Gaza militants fired two long-range rockets at Jerusalem for the first time since 1970.

The attack, which came an hour after the entrance of the Jewish Sabbath, was preceded by a siren that sounded in the city, as well as in surrounding communities, alerting civilians to take cover in protected spaces.

The projectiles exploded in open areas in Gush Etzion, a settlement bloc south of Jerusalem, causing no injuries or damage, local media reported, citing eyewitnesses.

Hamas's military wing, the Izz al-Din al-Qassam Brigades, swiftly claimed responsibility for the attack, claiming to have fired a homemade rocket it called Qassam M76.

"We are conveying a short and simple message: not a single Zionist on Palestinian soil is safe, and we're planning additional surprises," Ynet quoted Abu Ubaida, a spokesman for the group, was quoted as saying.

On Thursday night, rockets fired out of Gaza landed near the Tel Aviv municipal line and in the water off the Bat Yam shore, some 20 kilometers south of Tel Aviv, in the farthest such strikes by Hamas to date.

Iron Dome anti-missile batteries have intercepted nearly 200 rockets bound to hit populated areas since the fighting began, half of them on Friday, the army said.

Meanwhile, the Israeli Air Force (IAF) is shouldering the bulk of operations in Gaza and has targeted over 600 militant sites in a wave of raids.

The air strikes have thus far claimed 24 Palestinian fatalities, mostly civilians, and 270 wounded, Ynet reported, citing Hamas' Health Ministry officials.

Some 150 rocket stores, munitions caches and medium-range rocket launching sites were struck overnight Thursday, causing severe damage to Hamas's infrastructures, the army said.

A brief lull came Friday morning as Prime Minister Benjamin Netanyahu instructed the military to observe a one-sided, three- hour cease-fire during Egyptian Prime Minister Hesham Quandil's visit to Gaza that aimed to broker a truce.

The Egyptian official cut short the visit for an unknown reason, local media said.

Foreign Minister Avigdor Lieberman on Friday sought to reassure his counterparts around the world that Israel is going to great lengths to avoid casualties among the civilian populace along the Gaza Strip.

"We are doing everything possible to prevent the harming of innocent civilians in Gaza, while the Palestinians in Gaza continue to target Israeli civilians," Lieberman told the foreign ministers of Germany, Italy, Great Britain, France and Canada, according to a statement sent to Xinhua.

The foreign minister said Israel will not be content with a cease-fire that will break down "within a week or two" and intends to restore the kind of deterrence that will prevent the Palestinians from "employing terrorism" against Israel.