Successive Israeli evacuation orders in Gaza have displaced 90% of its 2.1 million residents since the Israel-Hamas war began in October, the top U.N. humanitarian official for the Palestinian territory says.

U.S. Vice President Kamala Harris says she and President Joe Biden are working to end the war in Gaza, where the International Rescue Committee says the polio virus has been circulating for the first time in a quarter-century because of the destruction of hospitals and water infrastructure, along with overcrowded living conditions.

White House national security spokesman John Kirby said Friday that cease-fire talks in Cairo have been constructive and will continue over the weekend. The United States, Egypt and Qatar are mediating the talks. A crucial sticking point involves Israel’s demand for lasting control over two strategic corridors in Gaza.

The war began on Oct. 7, when Hamas and other militants stormed Israel, killed around 1,200 people — mostly civilians — and abducted around 250. About 110 hostages are still inside Gaza, a third of whom are believed to be dead. The Israeli offensive launched in response has killed more than 40,000 Palestinians in Gaza, according to the local Health Ministry, which doesn't say how many were militants or civilians.