The death toll in Gaza climbed to 19, including five children, according to Palestinian health officials, as waves of Israeli fighter planes and drones sent missiles hurtling down on suspected weapons stores and rocket-launching sites. Smoke rises after Israeli air strikes in Gaza City on Friday. Credit:Reuters/Ahmed Zakot Early on Friday, 85 missiles exploded within 45 minutes in Gaza City, sending black pillars of smoke towering above the coastal strip's largest city. The military said it was targeting underground rocket-launching sites. One missile hit the Interior Ministry, a symbol of Hamas power, and another hit an empty house belonging to a senior Hamas commander.

Those strikes, together with an attack on a generator building near the home of Gaza's Hamas Prime Minister, Ismail Haniyeh, signalled that Israel was expanding its offensive beyond military targets. Israeli soldiers take cover as an air raid siren warns of incoming rockets before the funeral of Aaron Smadja, one of the three Israelis killed by a rocket fired from Gaza, in the southern town of Kiryat Malachi. Credit:AP/Tsafrir Abayov The fighting has already widened the instability gripping a region in the throes of war and regime upheavals. It has strained frayed relations with Egypt, which was sending its Prime Minister to Gaza on Friday in a show of solidarity with its militant Hamas rulers. Firefighters in Gaza try to extinguish a fire at the Ministry of Interior after it was hit by an Israeli missile on Friday. Credit:AFP/Marco Longari

Israel and Hamas had largely observed an informal truce since Israel's incursion into Gaza four years ago, but rocket fire and Israeli airstrikes on militant operations had not stopped entirely. The latest flare-up exploded into major violence on Wednesday when Israel assassinated Hamas's military chief and launched an air assault meant to cripple the militants' ability to terrorise Israel with rockets. The Israeli military reported early on Friday that its aircraft had struck more than 350 targets since the start of its operation against Hamas's rocket operations. After nightfall on Thursday, explosions shook Gaza City several minutes apart, a sign the strikes were not letting up. The military said the targets were about 70 underground rocket-launching sites.

The Israeli offensive has not deterred the militants from striking back – more than 400 rockets have been aimed at southern Israel. For the first time, they also unleashed the most powerful weapons in their arsenal – Iranian-made Fajr-5 rockets capable of reaching Tel Aviv. The two rockets that struck closest to Tel Aviv appear to have landed in the Mediterranean Sea, defence officials said, and another hit an open area on Tel Aviv's southern outskirts. No injuries were reported, but the rocket fire – the first in the area from Gaza – sowed panic in Tel Aviv and made the prospect of a ground incursion more likely. The government later approved the mobilisation of up to 30,000 reservists for a possible invasion.

The Israeli Prime Minister, Benjamin Netanyahu, said the army was hitting Hamas hard with what he called surgical strikes and he warned of a "significant widening" of the Gaza operation. Israel will "continue to take whatever action is necessary to defend our people," said Mr Netanyahu, who is up for re-election in January. At least 12 trucks were seen transporting tanks and armored personnel carriers towards Gaza on Thursday and buses were seen carrying soldiers towards the border. Israeli TV stations said a Gaza operation was expected on Friday, though military officials said no decision had been made. "We will continue the attacks and we will increase the attacks, and I believe we will obtain our objectives," said Lieutenant-General 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's 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. Much has changed since.

Israel has improved its missile defence systems but it is facing a more heavily armed Hamas. Israel estimates the militants have 12,000 rockets, including more sophisticated weapons from Iran and from Libyan stockpiles plundered after the fall of Muammar Gaddafi's regime last year. Also, regional alignments have changed dramatically since the last Gaza war. Hamas has emerged from its political isolation – its parent movement, the Muslim Brotherhood, has risen to power in several countries since last year's Arab uprisings, particularly in Egypt. Egypt recalled its ambassador to protest against the Israeli offensive and ordered its Prime Minister lead a senior delegation to Gaza on Friday in a show of support for Hamas.

While relations with Israel have cooled since the toppling of the Egyptian leader Hosni Mubarak, the new Islamist President, Mohammed Morsi, has not brought a radical change in Egypt's policy towards Israel. Loading 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. Associated Press