Israeli troops and tanks pushed deeper into Gaza on Monday, advancing on two sides of the territory’s main city, as the UN and medical staff warned that airstrikes have hit closer to hospitals where tens of thousands of Palestinians have sought shelter alongside thousands of wounded.

The UN agency for Palestinian refugees, known as UNRWA, says nearly 672,000 Palestinians are sheltering in its schools and other facilities across Gaza, which have reached four times their capacity. Some have been there for weeks, without knowing when they will be able to return home or if their homes have been demolished by airstrikes.

Video circulating on social media showed an Israeli tank and bulldozer in central Gaza blocking the territory’s main highway, which the Israeli military in recent weeks has suggested Palestinians use to evacuate to the south. Hundreds of thousands of Palestinians who remain in the north would no longer be able to escape if the road is blocked.

The video, taken by a local journalist, shows a car approaching an earth barrier across the road. The car stops and turns around. As it heads away, a tank appears to open fire, and an explosion engulfs the car. The journalist, in another car, races away in terror, screaming, “Go back! Go back!” at an approaching ambulance and other vehicles.

The Gaza Health Ministry later said three people were killed in the car that was hit. The Israeli military declined to comment on where its forces were deployed.

Israel said late on Monday that a female soldier captured by Hamas militants has been released during its ground operations in Gaza. The military provided few details, but she appears to be the first captive to be freed since Israel stepped up its ground war. The military says Private Ori Megidish “was medically checked, is doing well, and has met with her family.”

Hours earlier, the militant Hamas movement ruling Gaza released a short video on Monday purporting to show three women captured during its wide-ranging October 7 attack inside Israel, which triggered the war. One of the women delivers a brief statement, likely under duress, criticizing Israel’s response to the hostage crisis.

Hamas and other militants captured around 240 people during the deadly raid and have said they will release them in return for thousands of Palestinian prisoners held by Israel, including many implicated in deadly attacks on Israelis. Israel has dismissed the offer.

It was not clear when the video was made, but it was likely to add to the mounting domestic pressure on Israel’s leaders. Families of the captives who met with Prime Minister Benjamin Netanyahu over the weekend expressed support for an exchange.

The Associated Press usually refrains from reporting details of hostage videos because they show individuals speaking under duress and are often used for propaganda purposes.

The Israeli military has been vague about its operations inside Gaza, including the location and number of troops. But the movements of recent days, including stepped-up ground operations both north and east of Gaza City, combined with calls for residents to head south, point to a focus on the city.

Israel says much of Hamas’ forces and militant infrastructure, including hundreds of kilometers of tunnels, are in Gaza City, which before the war was home to over 650,000 people, a population comparable to that of Washington, DC.

Casualties on both sides are expected to rise sharply if Israeli forces expand their ground operation and end up battling Palestinian militants in dense residential areas.