Israeli strikes yesterday killed at least 48 people in the Gaza Strip, Palestinian health authorities said, as clashes took place in central and southern areas of the enclave ahead of the planned start of a polio vaccination campaign.

The United Nations is due to start vaccinating some 640,000 children in the territory against polio, relying on daily eight-hour pauses in fighting between Israeli forces and Hamas militants in specific areas of the besieged enclave.

Yousef Abu Al-Reesh, Gaza's deputy minister of health, said vaccination teams would try to get to as many areas as possible to ensure wide coverage but he said only a comprehensive ceasefire could guarantee enough children are reached.

"If the international community truly wants this campaign to succeed, it should call for a ceasefire, knowing that this virus does not stop, and can reach anywhere," he told reporters at Nasser Hospital in the southern city of Khan Younis.

Yesterday, medics administered vaccines on some of the children at Nasser Hospital wards in a symbolic move before the official campaign begins.

The campaign follows confirmation last week that a baby was partially paralysed by the type 2 polio virus, the first such case in the territory in 25 years.

WHO officials say at least 90 percent of the children need to be vaccinated twice with four weeks between doses for the campaign to succeed, but it faces huge challenges in Gaza, which has been largely destroyed by nearly 11 months of war.

As more than 2,000 medical and community workers prepared for the start of the campaign, medics in Nuseirat, one of the Gaza Strip's eight historic refugee camps, said separate Israeli strikes killed at least 19 people, including nine members of the same family.

More than 30 other people were killed in a series of strikes in other areas of Gaza, medics said.

The health ministry in Gaza yesterday said that at least 40,691 people have been killed since Israel began its offensive in October last year.

In the occupied West Bank, Israel pressed on with a large-scale military operation for a fourth day yesterday.

As clashes and explosions persisted in the northern city of Jenin, the Israeli military said two Palestinians were killed while preparing to carry out bombings overnight in the south of the West Bank.

At least 20 Palestinians have been killed by the Israeli army since Wednesday, most of them militants, in simultaneous raids in several cities in the northern West Bank.