Ground forces from Israel have entered the Gaza Strip in four different places, a week after its bombing offensive began and in spite of statements that a territorial incursion was not intended.
An Israeli military spokeswoman told the BBC and other agencies the intention of the latest military action, which has produced immediate condemnation around the world, was to take control of areas from which Palestinian militants have been firing rockets into Israel.
The Israelis had said that the aim of their bombing raids was to end the rocket attacks by Hamas-sponsored groups. But embarassingly, they failed to do so, even though claims of 'pinpoint accuracy' had been made.
In the past four days the Hamas rockets have not claimed any fatalities, while Israel's assaults have killed hundreds of Palestinians, belying claims of a 'proportionate response'.
The IDF accuses Hamas of hiding assailants in civilian buildings. But other analysts say that Gaza is so packed that it is difficult to demarcate.
Eyewitnesses say that Israeli armoured vehicles crossed into northern Gaza at four separate points, supported by helicopters. Earlier, Israel intensified air and artillery attacks on the territory.
France has strongly criticised the Israeli land campaign. The British Foreign Secretary, David Miliband, said the escalation of the conflict would cause alarm and dismay.
"We will not break, we will not surrender or give in to your conditions," declared Khaled Meshaal, the Hamas leader-in-exile.
In New York the UN Security Council is to hold a special meeting on the situation in Gaza early next week.
Israel has carried out more than 800 strikes on the Gaza Strip since the offensive started eight days ago, including 40 on Saturday 3 January.
The United Nations has warned of a worsening humanitarian crisis, and believes 25% of more than 400 Palestinians killed by Israel so far were civilians.