A line of Israeli tanks, some firing their weapons, have rolled into the northern Gaza Strip, a Palestinian witness has said.

The Israeli military confirmed that a force had entered Gaza to seize some areas used to launch rockets.

The witness, a resident of the Gaza town of Beit Lahiya, said the column crossed the boundary fence under cover of darkness, accompanied by Israeli combat helicopters.

The witness could not immediately say how far the Israelis had gone into Palestinian territory.

Israeli tanks and soldiers had been poised on the Gaza Strip border preparing for a possible ground offensive, as militants kept up rocket strikes on southern Israel in defiance of international calls for it to halt such attacks.

Foreign Minister Tzipi Livni said: "I hope the results of this operation will bring about quiet in the long term. The moment they fire, we will respond with great force."

Ms Livni added: "It could be that several operations will be needed."

Witnesses said an air strike on a mosque in the town of Beit Lahiya took place as people prayed inside. At least 11 civilians, including children, were killed and 50 wounded, Hamas and medical officials said.

Rescuers pulled people from the debris and the bodies of victims lay in pools of blood, the witnesses said.

Israel has targeted mosques before saying that Hamas had used them as command posts and fire bases.

The raid brought the Palestinian death toll to at least 446, with about 2,050 wounded, in the worst sustained bloodshed in decades of the conflict between Israel and the Palestinians.

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