Saudi Arabia has pledged $500 million to help rebuild Gaza, Palestinian Prime Minister Rami Al-Hamdallah said, with the full cost of post-war reconstruction expected to be around $4 billion over three years.

Saudi Arabia's commitment comes ahead of a conference in Cairo on October 12 when Palestinian leaders hope other donors, including Turkey, Qatar, the European Union and United States, will step forward with promises of support.

"Saudi Arabia has initiated donations by pledging $500 million," Hamdallah told reporters in Gaza, speaking via video conference from the West Bank. He said he hoped further pledges would cover the full cost of reconstruction in time.

An estimated 18,000 homes were destroyed during the seven-week war, while a further 40,000 were extensively damaged.

Major infrastructure such as roads, bridges and water treatment plants were heavily damaged, while Gaza's only power station will need almost entirely rebuilding. Dozens of factories on the outskirts of residential areas were extensively hit in artillery bombardments.

The war, which began on July 8 with Israel saying it was determined to put an end to rocket fire from Gaza, left more than 2,100 Palestinians dead, most of them civilians. Sixty-seven Israeli soldiers and six civilians were also killed.

Hamdallah's estimate is the latest of several that have put the cost of rebuilding the blockaded territory, home to 1.8 million people, at between $3 billion and $7.8 billion.

With so many homes destroyed, including at least three 14-story tower blocks, economists in Gaza estimate that 10,000 tonnes of cement a day will be needed over the next six months. That compares with the just 30 tonnes a week entering the territory before the war.

The ability to press ahead with reconstruction depends not just on raising the money but on Hamas, the Islamist faction that dominates Gaza, allowing the Palestinian Authority to resume civil administration and border controls in the enclave.

UN Middle East envoy Robert Serry said this week he had brokered a deal between the factions and with Israel that would allow the PA to take the lead on coordinating reconstruction, but it remains to be seen if it will work in practice.

Hamas and Fatah, which leads the Palestinian Authority, agreed in April to form a "unity government", but efforts to put that agreement into force have so far failed. Unless progress is made on forging a unity deal that works, donors are likely to be reluctant to commit money to Gaza.

"All donor countries have made a condition, they want to deal with the unity government," said Hamdallah. "If the government is not enabled in the Gaza Strip, there will be problems over reconstruction."

Mahmoud Al-Zahar of Hamas dismissed the unity government idea, describing it as a "government of failure", an indication of just how hard it will be to reconcile the factions and make progress on rebuilding Gaza. - Reuters