Smoke and flames erupt from an Israeli airstrike in Gaza City on Monday. (AP Photo/Jehad Alshrafi)

DEIR AL-BALAH, Gaza Strip (AP) — Israeli troops for the first time Monday pushed into areas of a central Gaza city where several aid groups are based, in what appeared to be the latest effort to carve up the Palestinian territory with military corridors.

Deir al-Balah is the only Gaza city that has not seen major ground operations or suffered widespread devastation in 21 months of war, leading to speculation that the Hamas militant group holds large numbers of hostages there. The main group representing hostages’ families said it was “shocked and alarmed” by the incursion and demanded answers from Israeli leaders.

Israel says the seizure of territory in Gaza is aimed at pressuring Hamas to release hostages, but it is a major point of contention in ongoing ceasefire talks.

The U.N. food agency, meanwhile, accused Israeli forces of firing on a crowd of Palestinians seeking humanitarian aid over the weekend. The Gaza Health Ministry called it one of the deadliest attacks on aid-seekers in the war that has driven the territory to the brink of famine.

In the latest sign of international frustration, the United Kingdom, France and 23 other Western-aligned countries issued a statement saying “the war in Gaza must end now.” They harshly criticized Israel’s restrictions on humanitarian aid and called for the release of the 50 hostages remaining in Gaza.

Evacuation orders dropped at dawn

Associated Press reporters heard explosions and saw smoke rising from parts of the city that were ordered evacuated on Sunday. The Israeli military official, speaking on condition of anonymity in line with regulations, said it was the first time ground troops had operated in the area.

A man living in the evacuation zone, who spoke on condition of anonymity for fear of retribution, said Israel dropped pamphlets at dawn ordering people to evacuate. Two hours later, tanks rolled into the area.

He said his 62-year-old father, who had spent the night elsewhere, fled from house to house as Israeli forces moved in and saw them flattening structures with bulldozers and tanks. Both men managed to leave the evacuation zone.

WHO says Israel raided its compound and detained staff

The World Health Organization said Israeli forces raided its main staff residence in Deir al-Balah, forcing women and children to evacuate on foot toward the coast.

“Male staff and family members were handcuffed, stripped, interrogated on the spot and screened at gunpoint,” the U.N. health agency said in a statement. It said two staff and two family members were detained, with three later released and one still being held.

The WHO said its main warehouse in the city, which is in the evacuation zone, was damaged by an explosion and a fire, hurting the agency’s ability to help hospitals and emergency medical teams. There was no immediate comment from the Israeli military.