We are ready for long weeks of action, says Israeli defence chief

Observers said that at least 10 people were killed and another 40 injured as up to 16 bombs were dropped by Israeli warplanes during early morning attacks.

The targets included the offices of Hamas prime minister Ismael Haniyeh, police stations and Gaza's treasury and foreign ministry buildings.

Sites linked to Hamas' military wing Izzadin Kazzam were also hit, including the home of the Gaza division commander.

The new offensive came despite calls by UN Secretary General Ban Ki-Moon and other world leaders for an immediate ceasefire and appeared to signal that the conflict will continue.

The death toll so far in Gaza is estimated at 320, with five Israeli fatalities, and hundreds of injuries.

As well as air strikes, Israel has also massed tanks, artillery and soldiers on the border with Gaza in preparation for a possible ground assault on the territory, with its defence minister warning that the country is engaged in a "war to the bitter end" against Hamas and its allied militant supporters.

Israel's deputy defence minister Matan Vilnai said today that his country was prepared for a prolonged struggle to protect its citizens from the repeated missile attacks which have been launched from the Gaza strip over recent months.

"The army is prepared for a long operation," he said. "We have made preparations for some long weeks of action."

Hamas said that its squads had fired 43 home-made rockets, 17 longer-range Grads and six mortar shells at Israel; other militant groups have also fired rockets at Israel.

UN Secretary-General Ban Ki-moon called for an immediate ceasefire and urged international leaders, including foreign ministers of the Arab League nations holding an emergency meeting Wednesday, to "act swiftly and decisively to bring an early end to this impasse".

He added that while Israel had a right to defend itself, its response to the missile attacks from Gaza amounted to an "excessive use of force", although he also condemned aggression by Hamas.

Further details emerged of earlier attacks by Israel against Hamas targets. A grainy video taken by an Israeli drone airplane showed several men loading a pickup truck with what the Israeli military said were medium-range Grad rockets. Moments later, a big explosion from an Israeli missile strike envelops the image.

In another air assault, an Islamic Jihad commander was killed walking near his house, said Abu Hamza, a spokesman for Islamic Jihad's military wing.