Shani Louk, a German-Israeli national, was among festivalgoers who had gathered in farmland near the Gaza-Israel border for what was supposed to be an all-night dance party celebrating the Jewish holiday of Sukkot.

Instead, in the early hours of Saturday morning, it was swarmed by Hamas fighters who gunned down revelers and took others hostage, as they launched an unprecedented assault on Israel.

Louk was later pictured in a video, identified by her dreadlocks and tattoos, being paraded through Gaza as onlookers shouted “Allahu Akbar.”

She is among a large number of Israeli nationals who have been taken hostage by Hamas militants and are now being held in locations across Gaza, complicating Israel’s response to the deadly attack.

Israel is taking pains to establish the exact number of hostages that have been taken into Gaza, an isolated coastal enclave of almost 2 million people crammed into 140 square miles, one of the most densely populated places in the world.

Lt. Col. Richard Hecht, the military’s international spokesperson, told CNN on Sunday that “dozens” had been captured and emphasized just how complex the situation was as the army launched air strikes on Gaza in retaliation. In an earlier briefing he had said “civilians, children and grandmothers” were among those being held captive.

Hamas claims it has captured dozens of Israelis, including soldiers, and videos authenticated by CNN show some of the dramatic seizures.

Al Qassam Brigades, the armed wing of Hamas, has warned attacks in the area could impact hostages, with its spokesman, Abu Obaida, saying in a recorded audio message Saturday that they were “present in all axes in the Gaza Strip.”

Lt. Col. Jonathan Conricus, an Israel Defense Forces (IDF) spokesperson, told CNN’s Wolf Blitzer that “it is unprecedented in our history that we have so many Israeli nationals in the hands of a terrorist organization.”

It has been more than 17 years since an Israeli soldier was taken as a prisoner of war in an assault on Israeli territory. And Israel has not seen this kind of infiltration of military bases, towns and kibbutzim since town-by-town fighting in the 1948 war of independence.