The United Nations on Monday said humanitarian work in the Gaza Strip has taken a serious blow after Israel ordered a new evacuation in the center of the besieged territory.

It came as the United States announced "progress" in Gaza truce talks under way in Cairo, even after a major but brief cross-border escalation between Israel and the Iran-backed Hezbollah group in Lebanon.

On Sunday the Israeli military ordered people to "evacuate immediately" a part of Deir el-Balah in central Gaza, sparking a rapid exodus of civilians and displacing U.N. and NGO workers.