Israel bombarded the Hamas-ruled Gaza Strip with nearly 200 airstrikes early Saturday, the country's military said, widening a blistering assault on militant rocket operations to include the prime minister's headquarters, a police compound and a vast network of smuggling tunnels.

Meanwhile, talks are continuing between several countries, including Egypt, Turkey, the U.S. and Russia, to try to find an end to the conflict.

Maj. Gen. Tal Russo, Israel's southern commander, said Saturday that Hamas had suffered a tough blow.

"Most of their capabilities have been destroyed," he told reporters. Asked whether Israel is ready to send ground troops into Gaza, he said: "Absolutely."

The military also said its air defences had shot down a rocket fired at Tel Aviv — marking the third day in a row that Hamas militants have launched an attack at Israel's largest city. Air-raid sirens blared in the coastal metropolis during the day and explosions could be heard.

Hamas said the rocket was an Iranian-made Fajr 5.

The White House said on Saturday that President Barack Obama has been in touch with the Egyptian and Turkish leaders. Speaking on Air Force One, deputy national security adviser Ben Rhodes said that the White House believes Israel "has the right to defend itself" against attack and that the Israelis will make their own decisions about their "military tactics and operations."

The new attacks followed Friday's unprecedented rocket strike aimed at the contested holy city of Jerusalem that raised the stakes in Israel's violent confrontation with Palestinian militants and dramatically extended the battlefield.

Israeli aircraft on Saturday were also still pounding their original targets, the militants' weapons storage facilities and underground rocket launching sites. They also went after rocket squads more aggressively.

Invasion looms

"It was a very, very violent night in Gaza last night," CBC reporter Sasa Petricic said from Israel. He said the first major wave of bombings started around 3 a.m. local time, followed by another round at 5 a.m.

"The Israelis came in with their aircraft, with their bombs and their missiles," targeting most of the Hamas cabinet offices in Gaza and the home of at least one senior official, Petricic said.

"Just to give you a sense of the scale of this, in the first three days of this heightened conflict, Israel sent in something like 600 missiles. Well, just last night alone, in fact within a few hours, they sent in something like 200 more."

The Israeli military has called up thousands of reservists and massed troops, tanks and other armoured vehicles along the border with Gaza, signalling a ground invasion could be imminent. The armoured units are deployable on an hour's notice.

Militants, undaunted by the heavy damage the Israeli 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 the Tel Aviv heartland.

Following those attacks, the military deployed what it calls an "Iron Dome" rocket defence battery in central Israel on Saturday. The system, devised precisely to deflect the Gaza rocket threat, was deployed two months earlier than planned, the Defence Ministry said.

Nine people, including eight militants, were killed and dozens were wounded in the various attacks early Saturday, Gaza health official Ashraf al-Kidra said. In all 42 Palestinians, including 13 civilians, and three Israeli civilians have been killed since the Israeli operation began.

Tunisian minister visits

The violence has widened the instability gripping the Mideast. At the same time, revolts against entrenched regional regimes have opened up new possibilities for Hamas. Islamists across the Mideast have been strengthened, bringing newfound recognition to Hamas, shunned by the international community because of its refusal to renounce violence against Israel.

A high-level Tunisian delegation, led by Foreign Minister Rafik Abdessalem, drove that point home when it defied the fighting and arrived in Gaza on Saturday. His first stop was the still-smouldering ruins of Prime Minister Ismail Haniyeh's demolished headquarters.

It was the first official Tunisian visit since Hamas's violent 2007 takeover of the territory. Egypt's prime minister visited Friday and a Moroccan delegation is due on Sunday, following a landmark visit by Qatar's leader last month that implied political recognition.

Israel had been incrementally expanding its operation beyond military targets but before dawn on Saturday it ramped that up dramatically, hitting Hamas symbols of power. Israeli defence officials, speaking on condition of anonymity to discuss confidential decisions, said military chief Lt.-Gen. Benny Gantz personally ordered the scope of the airstrikes to be increased.

Haniyeh's three-story office building was flattened by an airstrike that blew out windows in neighbouring homes. He was not inside the building at the time.

A man looks over the damage to a house near the southern Israeli city of Ashdod on Saturday. The home was hit by a rocket fired by Palestinian militants in Gaza. (Amir Cohen/Reuters)

The building's security chief said Hamas scored points despite Israel's military superiority.

"Hamas responded to the Zionist aggression and hit them in the depth of their land," he said, referring to rockets aimed Friday at Jerusalem and Tel Aviv.

Another airstrike brought down the three-story home of a Hamas commander in the Jebaliya refugee camp near Gaza City, critically wounding him and injuring other residents of the building, medics said.

Missiles smashed into two small security facilities and the massive Hamas police headquarters in Gaza City, setting off a huge blaze that engulfed nearby houses and civilian cars parked outside, the Interior Ministry reported. No one was inside the buildings.

The Interior Ministry said a government compound was also hit while devout Muslims streamed to the area for early morning prayers, although it did not report any casualties from that attack.

Power knocked out

Air attacks knocked out five electricity transformers, cutting off power to more than 400,000 people in southern Gaza, according to the Gaza electricity distribution company. People switched on backup generators for limited electrical supplies.

In southern Gaza, aircraft went after underground tunnels militants use to smuggle in weapons and other contraband from Egypt, residents reported. A huge explosion in the area sent buildings shuddering in the Egyptian city of El-Arish, 45 kilometres away, an Associated Press correspondent there reported.

Israeli air strikes in Gaza City on Saturday sent up smoke and flames. Military jets pounded Hamas government buildings in the coastal territory. (Suhaib Salem/Reuters)

The Israeli military said more than 800 targets have been struck since the operation began.

The widened scope of targets brings the scale of fighting closer to that of the war the two groups waged four years ago. Hamas was badly bruised during that conflict, 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 fighting Israel.

The attack aimed at Jerusalem on Friday and two strikes on metropolitan Tel Aviv showcased the militants' new capabilities, including a locally made rocket that appears to have taken Israeli defence officials by surprise. Both areas had remained outside the gunmen's reach before.

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.

Israeli leaders have threatened to widen the operation even further if the rocket fire doesn't halt. Foreign Minister Avigdor Lieberman said options included the possible assassination of Haniyeh, the prime minister.

The Israeli Cabinet approved mobilizing up to 75,000 reservists, more than doubling the number authorized earlier this week. That would be the largest call-up in a decade.