No-one knows how many people have been killed
Two villages around Ramallah were the latest targets of Israeli tanks and helicopter-borne troops, eyewitnesses said on Sunday morning.
Israeli Prime Minister Ariel Sharon told him on the phone later that Israel would speed up, but not stop, its offensive against Palestinian militants.
The Israeli army's chief spokesman, Brigadier-General Ron Kitrey, said no new orders had been received and the operation was "going ahead as planned".
It is not known how many people have been killed in the Israeli offensive, but correspondents say Israeli gunships have been firing into crowded refugee camps where there are no means of escape.
There are reports of heavy and continuous shelling of the town of Nablus in the northern West Bank, where the historic old city is surrounded by Israeli troops and gunman are dug in in the dense maze of streets and alleyways.
The US president demanded an immediate Palestinian ceasefire and a crackdown on "terrorist networks". He condemned Palestinian leader Yasser Arafat for "failing his people".
US Secretary of State Colin Powell is due to arrive in the region on Monday, but will not reach Israel until later and has said he has no plans to meet Mr Arafat.
"Where is Powell?" asked Palestinian Local Government Minister Saeb Erekat in one interview, in which he accused Mr Sharon of "using the time between now and the arrival of Powell to destroy everything."
Ambulances 'obstructed'
Statements from Mr Sharon's office said he promised to "expedite" the operation, but it was being prolonged by Israel's "policy preventing harm to civilians".
An Israeli army spokesman told Israeli radio the operation in Jenin could end on Sunday.
Residents at the Jenin refugee camp said they feared a "massacre" was taking place. Palestinian Information Minister Yasser Abed Rabbo told AFP that 35 Palestinians were dead and hundreds injured in the town.
A Palestinian doctor told the BBC that Israel was firing heavy weaponry from the hills around the town and that ambulances had been unable to reach the dead and wounded.
UN relief workers said a convoy of food aid had reached Nablus but they could not distribute it because of the security situation.
On Saturday night, people in both Jenin and Nablus were reported to have been left without electricity or running water.
Tanks also entered the refugee camp of Fawar, south of Bethlehem, where a 13-year-old boy was killed.
Israeli air force commander Dan Halutz told a news conference that seven soldiers had been killed over the past two days in the town.
Several thousand Israeli peace campaigners gathered in Tel Aviv on Saturday night under the slogan "End occupation, start negotiation". But opinion polls show that Israelis, rocked by suicide bombings that have deepened fears that no place in Israel is safe, overwhelmingly support the operation.
The stand-off at the Church of the Nativity in Bethlehem, where hundreds of Palestinians are besieged by Israeli forces, has continued into its sixth day.
Vatican diplomats denied reports that they put forward a proposal to Israelis and Palestinians to end the stalemate at the church, one of Christianity's holiest sites.