Israeli warplanes killed 10 Palestinians today in attacks that targeted Hamas government buildings and other symbols of the Islamist group on the fourth day of the fiercest air offensive in Gaza in decades.

Israeli missiles flattened five ministerial buildings and a structure belonging to the Islamic University in Gaza City, witnesses said.

Muawiyah Hassanein, the head of Gaza City's ambulance department, said security guards and civilians were among those killed.

A Hamas sports centre and two training camps belonging to the group were also destroyed in the attacks, which plunged Gaza into a blackout as explosions echoed across the city.

Medical officials put the total Palestinian death toll at 345 and more than 800 wounded. A United Nations agency said at least 62 of the dead were civilians.

The latest attacks came hours after rockets fired by Gazan militants killed an Israeli soldier at a military base near the border with Gaza and a civilian in the city of Ashdod. The Israeli army also amassed armoured forces along the frontier.

Israeli aircraft also fired missiles at the home of a senior commander in Hamas's armed wing. He was not home. Another attack targeted offices belonging to the Popular Resistance Committees militant group.

Broadening their targets to include the Hamas government in Gaza, Israeli warplanes yesterday bombed the Interior Ministry, which supervises 13,000 members of the group's security forces. The building had been evacuated and there were no casualties.

Hamas, an Islamist movement that took over the Gaza Strip in 2007 after routing Fatah forces loyal to President Mahmoud Abbas, defied the Israeli assaults, the fiercest in the coastal territory since the 1967 Middle East war.

Rocket fire from Gaza at Israel intensified immediately after Hamas declared the end of an Egyptian-brokered, six-month-old truce on December 19.

With six weeks to go to an election that polls suggest the hawkish right-wing Likud party will win, Israel's centrist government says the offensive aims to put a stop to the rockets.

Four Israelis have been killed by rockets since the offensive began four days ago, including three yesterday.

Israel declared areas around the Gaza Strip a "closed military zone", citing the risk from Palestinian rockets, and ordered out journalists observing a build-up of armoured forces.

Excluding the press could help Israel conceal preparations for a ground incursion following an air campaign that has turned buildings to rubble and left hospitals struggling to cope.