(NewsNation) — Following a surprise attack on Israel, Hamas claims it is now holding more than 100 Israelis as hostages. Abbey Onn, an American living in Israel, says five of her family members are among the hostages, and that they’re “scared for their lives.”

Onn told “On Balance” host Leland Vittert that she lost contact with the family members on Saturday after messaging with them.

“We woke up Saturday like everyone else in Israel to sirens, and we thought that it was the regular, you know, run of the mill war. We have family in the center and the north and the south, and so we all started speaking on WhatsApp. We quickly understood that our family … in a kibbutz close to Gaza, had been infiltrated by Hamas,” Onn said. “And we were getting text messages that they were in the house and that they could hear gunfire, and that they were scared for their lives.”

Onn says she then watched footage posted online that shows her 12-year-old cousin being abducted.

“We have video of Erez, who is 12, in the hands of Hamas,” Onn told Vittert, later adding: “I have three children the same age as these children who were kidnapped, and it’s a parent’s worst nightmare.”

Onn identified her missing family members as Carmela Dan, Ofer Kalderon, Sahar Kladeron, Erez Kalderon and Noya Dan.

“(To) my family, I want them to know that we love them, and we’re doing anything we can to get them safely returned,” Onn said. “And to the kidnappers and anyone else who can understand this, I want them to think of their own family, of their mother and their father and their sister and their brother and their grandmother, and think what that would be (like) if they were in the hands of terrorists. It’s horrifying.”

Dori Roberts is also among those who have no idea if his family in Israel is safe following the incursion.

Roberts does not know where his cousin and her two young daughters are, as well as his aunt and aunt’s longtime partner. Roberts assumes they were kidnapped.

“They woke up to a nightmare, a terror, sirens all over the place, explosions, shots were fired. They were in the safe room locked, in fear for their lives, learning on the information groups that there are terrorists in the community that is really only about a mile away from the Gaza border,” Roberts told NewsNation host Chris Cuomo.

Roberts last heard from his loved ones Saturday morning before all communication was lost.

“We assumed they were kidnapped and soon after, we saw the video coming from the Hamas showing my cousin, my aunt and the two kids being taken on a vehicle surrounded by armed Hamas militants to the Gaza Strip,” Roberts said.

Yifat Zailer fears for the life of her family members, as well. She says her cousin, cousin’s husband, their two young children and aunt and uncle were also kidnapped in Israel by Hamas.

Like Onn and Roberts, Zailer discovered her family had been taken captive through a video posted online.

“There’s a video of her holding her two little babies outside her house, in the kibbutz where she lives. This is how I found out about it. This is how our sister found out about it. Her sister lives in a different kibbutz. She was in a safe room, watching her sister being kidnapped,” Zailer told Cuomo.

She added: “I fear for their lives. I fear for the babies, if they’re being fed. My aunt has Parkinson’s disease (…) We’re in the dark. We need to force them (Hamas) to show us their faces, that they’re alive, something. It’s a catastrophe.”

As for Onn, she does not believe people in the U.S. fully understand the scope of the situation.

“Look, this is our 9/11. This is the never coming back from moments in Israel. When it happened in America, it was a very clear-cut issue. Here, it’s not that way,” Onn said. “We need people to understand that this is terror. This is ISIS. This is exactly the threat that we had in the U.S., you know, 20-something years ago, and we need the international community to respond the same way.”

As violence in southern Israel rages on, Hamas has reportedly threatened to execute Israeli hostages if Israel continues to bomb the Gaza Strip without warning Palestinian civilians. Meanwhile, the National Security Council is “publicly calling for Hamas to release every single hostage in their possession.”

Sunday evening, Israel Defense Forces spokesperson Lt. Col. Jonathan Conricus told “NewsNation Prime” he could not “offer any words of support or any promises” to families of hostages.

“At this stage with this extremely delicate matter, I cannot offer any words of support or any promises. We’re dealing with a murderous organization that we know has no respect for human life,” Conricus said.

Hamas fighters launched a surprise attack on Israel over the weekend. On Sunday, Israel formally declared war. The war’s death toll has risen to nearly 1,600 on both sides. U.S. officials confirmed at least 11 Americans are among the dead.

The Associated Press contributed to this report.